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BACKGROUND: Multidrug resistance related proteins (MRP-proteins), members of the ATP binding cassette (ABC-) superfamily, are known to play an important role in regulation of glutathione homeostasis within cells, and hence in GSH dependent transport processes of xenobiotics. Many airborne compounds are hazardous inducing inflammatory reactions in lung and are suspected to play a substantial role in initiation and/or promotion of tumor formation. It is interesting to clarify whether and how anti-prostaglandins modify MRP function in normal human lung cells. Aspirin, an acetylated salicylate, is classified among the non-steroidal anti-inflammatory drugs (NSAIDs), reduce inflammatory signs and symptoms exhibiting a broad range of pharmacological activities (analgesic, antipyretic and antiplatelet properties). Cyclooxygenase (COX)-system catalyses the rate limiting step in prostanoids (prostaglandin (PG)) synthesis and is also involved in drug resistance and poor prognosis of many neoplastic diseases. Aspirin's ability to suppress prostaglandins and thromboxanes production is due to its irreversible inactivation of the cyclo-oxygenase (COX) enzyme. Furthermore, transport activity study of MRP1 in NHBEC, PLC and A549 under the effect of exogenously supplied PGE2 showed an increased activity. METHODOLOGY and RESULTS: In this study, both the localisation and description of the cellular distribution of MRP-1 under standard culture conditions in normal human bronchial epithelial cells (NHBEC), peripheral lung cells (PLC) and tumor lung cells (A549) was proved using indirect immunofluorescence microscopy. All substrates and incubation periods have been pre-checked for cellular toxicity in the MTT assay in order to guarantee that non toxic conditions are applied. CONCLUSION: COX inhibitor (acetylsalicylic acid 1,2mM) could significantly decrease the transport activity of MRP1 in NHBEC, PLC and A549 in 1 and 3 days trials.

Lead (Pb) exposure of consumers and the environment has been reduced over the past decades. Despite all measures taken, immission of Pb onto agricultural soils still occurs, with fertilizer application, lead shot from hunting activities, and Pb from air deposition representing major sources. Little is known about the intermediate and long-term consequences of these emissions. To gain more insight, we established a mathematical model that considers input from fertilizer, ammunition, deposition from air, uptake of Pb by crops, and wash-out to simulate the resulting Pb concentrations in soil over extended periods. In a further step, human oral exposure by crop-based food was simulated and blood concentrations were derived to estimate the margin of exposure to Pb-induced toxic effects. Simulating current farming scenarios, a new equilibrium concentration of Pb in soil would be established after several centuries. Developmental neurotoxicity represents the most critical toxicological effect of Pb for humans. According to our model, a Pb concentration of ~ 5 mg/kg in agricultural soil leads to an intake of approximately 10 µg Pb per person per day by the consumption of agricultural products, the dose corresponding to the tolerable daily intake (TDI). Therefore, 5 mg Pb/kg represents a critical concentration in soil that should not be exceeded. Starting with a soil concentration of 0.1 mg/kg, the current control level for crop fields, our simulation predicts periods of ~ 50 and ~ 175 years for two Pb immission scenarios for mass of Pb per area and year [scenario 1: ~ 400 g Pb/(ha × a); scenario 2: ~ 175 g Pb/(ha × a)], until the critical concentration of ~ 5 mg/kg Pb in soil would be reached. The two scenarios, which differ in their Pb input via fertilizer, represent relatively high but not unrealistic Pb immissions. From these scenarios, we calculated that the annual deposition of Pb onto soil should remain below ~ 100 g/(ha × a) in order not to exceed the critical soil level of 5 mg/kg. We propose as efficient measures to reduce Pb input into agricultural soil to lower the Pb content of compost and to use alternatives to Pb ammunition for hunting. Electronic supplementary material The online version of this article (10.1007/s00204-020-02762-x) contains supplementary material, which is available to authorized users.

The use of hydraulic fracturing (HF) to extract oil and natural gas has increased, along with intensive discussions on the associated risks to human health. Three technical processes should be differentiated when evaluating human health risks, namely (1) drilling of the borehole, (2) hydraulic stimulation, and (3) gas or oil production. During the drilling phase, emissions such as NOx, NMVOCs (non-methane volatile organic compounds) as precursors for tropospheric ozone formation, and SOx have been shown to be higher compared to the subsequent phases. In relation to hydraulic stimulation, the toxicity of frac fluids is of relevance. More than 1100 compounds have been identified as components. A trend is to use fewer, less hazardous and more biodegradable substances; however, the use of hydrocarbons, such as kerosene and diesel, is still allowed in the USA. Methane in drinking water is of low toxicological relevance but may indicate inadequate integrity of the gas well. There is a great concern regarding the contamination of ground- and surface water during the production phase. Water that flows to the surface from oil and gas wells, so-called ‘produced water’, represents a mixture of flow-back, the injected frac fluid returning to the surface, and the reservoir water present in natural oil and gas deposits. Among numerous hazardous compounds, produced water may contain bromide, arsenic, strontium, mercury, barium, radioactive isotopes and organic compounds, particularly benzene, toluene, ethylbenzene and xylenes (BTEX). The sewage outflow, even from specialized treatment plants, may still contain critical concentrations of barium, strontium and arsenic. Evidence suggests that the quality of groundwater and surface water may be compromised by disposal of produced water. Particularly critical is the use of produced water for watering of agricultural areas, where persistent compounds may accumulate. Air contamination can occur as a result of several HF-associated activities. In addition to BTEX, 20 HF-associated air contaminants are group 1A or 1B carcinogens according to the IARC. In the U.S., oil and gas production (including conventional production) represents the second largest source of anthropogenic methane emissions. High-quality epidemiological studies are required, especially in light of recent observations of an association between childhood leukemia and multiple myeloma in the neighborhood of oil and gas production sites. In conclusion, (1) strong evidence supports the conclusion that frac fluids can lead to local environmental contamination; (2) while changes in the chemical composition of soil, water and air are likely to occur, the increased levels are still often below threshold values for safety; (3) point source pollution due to poor maintenance of wells and pipelines can be monitored and remedied; (4) risk assessment should be based on both hazard and exposure evaluation; (5) while the concentrations of frac fluid chemicals are low, some are known carcinogens; therefore, thorough, well-designed studies are needed to assess the risk to human health with high certainty; (6) HF can represent a health risk via long-lasting contamination of soil and water, when strict safety measures are not rigorously applied.

The excessive release of reactive nitrogen compounds into the environment is one of the biggest ecological problems of our time. Stefanie Jung, Jan Wiese, Heidi Foth, Manfred Niekisch The largest single source of nitrogen emissions is the agricultural sector, whereas livestock production chains are responsible for a high proportion of nitrogen losses. Changing meat consumption patterns is imperative for sustainable consumption. The topic polarises public opinion. We argue for the development of a mix of policy measures to promote environmentally compatible food consumption, with special emphasis on the (reduced) release of reactive nitrogen.

The release of reactive nitrogen compounds into the atmosphere, soil and water belongs to one of the biggest environmental challenges in Germany. Consequences are the loss of biodiversity due to eutrophication and acidification of terrestrial and aquatic ecosystems, impaired groundwater quality and impacts on human health. Responsible for the emissions of reactive nitrogen compounds are primarily agricultural activities and combustion processes. A number of European environmental targets and objectives in the context of nitrogen are clearly being missed. It is urgently necessary to increase the efforts to reduce nitrogen emissions and to protect biodiversity and human health. Important processes are a further development of European clean air policies and the implementation of the European Nitrate Directive and Water Framework Directive in Germany. A national nitrogen strategy could be a good starting point to increase efforts to solve the nitrogen problem and for a better integration of existing protection policies.

Arsenic is a human carcinogen that occurs ubiquitously in soil and water. Based on epidemiological studies, a benchmark dose (lower/higher bound estimate) between 0.3 and 8 μg/kg bw/day was estimated to cause a 1 % increased risk of lung, skin and bladder cancer. A recently published study by EFSA on dietary exposure to inorganic arsenic in the European population reported 95th percentiles (lower bound min to upper bound max) for different age groups in the same range as the benchmark dose. For toddlers, a highly exposed group, the highest values ranged between 0.61 and 2.09 µg arsenic/kg bw/day. For all other age classes, the margin of exposure is also small. This scenario calls for regulatory action to reduce arsenic exposure. One priority measure should be to reduce arsenic in food categories that contribute most to exposure. In the EFSA study the food categories 'milk and dairy products,' 'drinking water' and 'food for infants' represent major sources of inorganic arsenic for infants and also rice is an important source. Long-term strategies are required to reduce inorganic arsenic in these food groups. The reduced consumption of rice and rice products which has been recommended may be helpful for a minority of individuals consuming unusually high amounts of rice. However, it is only of limited value for the general European population, because the food categories 'grain-based processed products (non rice-based)' or 'milk and dairy products' contribute more to the exposure with inorganic arsenic than the food category 'rice.' A balanced regulatory activity focusing on the most relevant food categories is required. In conclusion, exposure to inorganic arsenic represents a risk to the health of the European population, particularly to young children. Regulatory measures to reduce exposure are urgently required.

Activation of poly(ADP-ribose) polymerase-1 (PARP-1) in response to DNA damage is an important mechanism to keep homeostasis or to trigger apoptosis. The expression and function of (PARP-1) was studied in primary cells cultured from human lung. Normal human bronchial epithelial cells (NHBEC) and peripheral lung cells (PLC) from lung cancer patients were grown as explant cultures and were followed over a period of 12 weeks. PARP-1 protein was expressed in all explant cultures from bronchial epithelium. The levels of PARP protein differed between individuals by a factor of 2.3 in the first explant. Three cases were followed for more than 100 days. The expression levels varied intra-individually by a factor of 1.3-1.4 over this time period. PARP-1 activity was determined immunohistochemically after induction of DNA damage with H(2)O(2) (0.05-0.3 mM, 5 min). The fluorescence signal for ADP-ribose polymers attached to chromatin proteins correlated well with the concentration of H(2)O(2). PARP-1 activity differed by a factor of 3.1 in NHBECs obtained from the first generation of explants from 11 cases. PARP-1 activity is present in NHBECs until the 8th and in PLCs until the 12th week and declined to about half of the start level. Primary cultures of NHBECs and PLC are suitable to study the effect of external factors on PARP-1 expression and function.

Nach Inkrafttreten der neuen EU-Chemikalienverordnung (REACH) wird eine neue Institution, die Europaische Agentur fur chemische Stoffe (ECHA) als zentrale Registrierungsbehorde eingerichtet, um alle administrativen Stufen der Chemikalienregulierung auf die Gemeinschaftsebene zu ubertragen. Die Agentur wird von einem Direktor geleitet, das ihm unterstehende Sekretariat nimmt alle zentralen Aufgaben wahr. Ihr gehoren ferner der Verwaltungsrat, der Ausschuss fur Risikobeurteilung, der Ausschuss fur soziookonomische Analyse und der Ausschuss der Mitgliedsstaaten sowie das Forum und die Widerspruchskammer an. Die Agentur ist fur die Verwaltung sowie Durchfuhrung vieler entscheidender Aspekte innerhalb von REACH zustandig und gibt den EU-Mitgliedsstaaten sowie der Europaischen Kommission, dem Europaischen Rat und Parlament den bestmoglichen technischen und wissenschaftlichen Rat in Bezug auf Fragen zu chemischen Substanzen. Die Novelle unter REACH integriert vereinfachte Bewertungsverfahren, Flexibilisierungen und Arbeitserleichterungen im Prufaufwand sowie gestraffte Ablaufe, um den benotigten Beschleunigungseffekt bei der Substanzprufung und Bewertung zu ermoglichen. Es hat bislang kein vergleichbares Verfahren zur Regulierung chemischer Substanzen gegeben, das einen derart grosen Arbeitsaufwand in so kurzer Zeit unter neuen organisatorischen Bedingungen und mit erweiterten Inhalten zu bewaltigen hat.

Unter der europaischen Chemikalienverordnung REACH (EG 1907/2006) sollen Informationslucken zu Eigenschaften chemischer Substanzen geschlossen werden. Diese Informationen werden auch fur andere regulierte Bereiche, zum Beispiel fur den Arbeitsschutz und die Produktionssicherheit, benotigt. Das Wissen, das auf Basis bisheriger Regulierungen gewonnen wurde, muss verbreitert werden, da sich diese Bewertungen meist nur auf Substanzen mit grosen Produktionsvolumina konzentrierten. Die bisherigen Beurteilungsverfahren nahmen zu viel Zeit in Anspruch und mussen fur die Mehrzahl der Substanzen gestrafft und dennoch vollzugssicher ausgestaltet werden. Hersteller und Importeure erhalten die Pflicht zur Registrierung ihrer Substanzen unter Vorlage von Daten. Die Verantwortlichkeit bei der Evaluation von Risiken wird auf Hersteller und Importeure ubertragen, und die Behorden werden von primaren Bewertungsaufgaben entlastet. Die Teststrategien zur Beurteilung von Risiken durch Substanzen schliesen Alternativen zum Tierversuch ein. Die fur die Registrierung bereitgestellten Daten und Bewertungen sollen die Europaische Agentur fur chemische Stoffe (ECHA) in die Lage versetzen, besonders gefahrliche chemische Substanzen zu identifizieren. In der Autorisierung soll der Umgang mit ihnen kontrolliert und begrenzt werden.

Queen pheromones interfere with worker reproduction in social insects. However, there is still an unresolved question as to whether this pheromone acts as an “honest” signal for workers, giving a reliable indication of the queen’s reproductive value, or as a suppressive agent, inhibiting worker reproduction independent of the queen’s reproductive capacity. In honeybees (Apis mellifera), the queen’s mandibular gland secretion, a mix of fatty acids and some aromatic compounds, is crucial for regulating the reproductive division of labor in the colony inhibiting ovary development in workers. We quantified the mandibular gland secretions of virgin, drone-laying, and naturally mated queens using gas chromatography to test whether the queens’ mating, ovary activation, or the reproductive value for workers correlated with the composition of the secretion. Although the absolute amounts of the “queen substance” 9-oxo-2(E)-decenoic acid (9-ODA) were similar among the three groups, the proportions of 9-ODA decreased with increasing reproductive quality. Furthermore, the ratios of queen to worker compounds were similar in all three treatment groups, irrespective of the reproductive capacity. A multivariate analysis including all six compounds could not separate drone-laying queens from naturally mated ones, both with active ovaries but only the latter ensuring colony survival. We suggest that the mandibular gland pheromones are unlikely to function as reliable indicators of queen reproductive value and rather operate as an agent to suppress worker reproduction. This does not exclude the possibility that other “honest” pheromone signals exist in the honeybee colony, but these would have to arise from other semiochemicals, which could be produced by both the queen and the brood.

Currently, comprehensive toxicological data are available only for a small percentage of the 30,000 substances produced in volumes of 1-100 tons per year in the EU. Substances with inadequate safety data sets may pose a risk to employees, consumers and the environment. To improve this unsatisfactory situation the European Commission put forward a draft concept that will probably become law in 2006. The acronym of this concept is REACH standing for Registration, Evaluation and Authorization of Chemicals. The aim of REACH is to systematically evaluate the risk of approximately 30,000 chemical substances produced, used or imported in quantities of 1-100 tons per year. From a practical point of view the testing requirements for these chemicals are one of the most important parts of the REACH proposal. The latter progressively increase with the volume of chemical substances, including, e.g. acute, subchronic and chronic toxicity tests. Without doubt REACH will provide an important contribution to health protection for workers and consumers. But perhaps even more importantly, REACH offers an opportunity to optimize and innovate testing strategies for chemicals. Such novel techniques are in particular RNA expression profiling, proteome analysis and metabonomics to describe alterations in gene or protein expressions patterns or in metabolite concentrations in response to toxic stimuli. Promising data have been published indicating that these techniques might identify hepato- or nephrotoxic compounds or even carcinogens differentiating between genotoxic and non-genotoxic substances. However, so far only a relatively small number of selected typical substances with well known toxic mechanisms has been tested. Therefore, the most promising innovative techniques should be optimized and validated by investigating a series of other typical but also untypical substances. In a further step a supplementary research program to REACH should be launched including promising innovative techniques (e.g. genomics, proteomics, metabonomics) but also other alternative methods (e.g. in vitro or QSAR), concentrating on the same substances that have to be tested by conventional animal studies in the mandatory part of REACH. In the present review we summarize key features of REACH, and discuss possibilities for the development of improved techniques and integrated strategies for toxicity testing.

Defense against toxic endo- and xenobiotics is a major concern of all living species and ABC transporters play a vital role in this defense system. Multidrug resistance associated proteins 1 (MRP1) is a cellular detoxifying factor supposed to transport a wide range of compounds across cell membranes either as GSH conjugates or as co-transport accompanying glutathione transposition. The cellular localization of MRP1 is a determining factor whether the transport function can take place. In this study we have undertaken experiments on the transport activity of MRP1 in cultured human lung tumor cells in order to check whether MRP1 is expressed as a functionally active protein. For this purpose we have adapted a quantitative fluorescence imaging assay to conditions where a small number of attached cells should be repeatedly measured by a non-destructive method. In cultured A549, H358 and H322 cells MRP1 is located in the cell membrane as observed by immunocytochemistry. Efflux of 5,6-carboxy-2'-7'-dichloro-fluorescein (CDF) from lung cells was sensitive toward the MRP1 inhibitor MK571 while verapamil had no effect. On the other hand, efflux of Rhodamin 123, a Pgp-glycoprotein substrate, from lung cells reacted to inhibition by verapamil, while MK571 had no effect. Modulation of glutathion content of lung cells by N-acetyl cystein and buthionine sulfoximine shifted CDF efflux toward higher or lower rates, respectively. These experiments confirm that MRP1 function can be followed in the attached cells in vitro under non-toxic concentrations of the substrates without the need to harvest and destroy the cells.

Transport processes form part of the body's defense mechanism, and they determine the intracellular levels of many endogenous and exogenous compounds. The multidrug resistance-related protein MRP1 and the lung resistance-related protein LRP are associated with drug resistance against chemotherapeutics; they protect cells against toxic compounds. There is much experimental evidence to suggest that both of these transporter proteins serve important physiological functions. The expression of LRP and MRP1 was studied in normal human bronchial epithelial cells (NHBEC) and peripheral lung cells (PLC) obtained from explant cultures from morphologically-normal human lung tissue taken from patients with lung cancer. LRP (mRNA and protein) was detected in the cells of the bronchi as well as the peripheral lung with low (a factor of 2.6) inter-individual variation in the first generation. No significant alterations were noted for LRP within three-to-four generations in the same patient. LRP expression was not substantially different between cultures from different topographic regions of the human lung. MRP1 protein and MRP1 mRNA could also be detected in all of the NHBEC and PLC cultures studied, but with substantially higher (a factor of 7.7) intra-individual variation in the first generation than for LRP. MRP expression was the same for bronchial cells and PLC when the material was obtained from both sites. The level of mRNA for MRP1 was, in general, less stable than that for LRP. In multigeneration explant cultures, the levels of LRP mRNA and protein and MRP1 protein did not fluctuate greatly, but the level of MRP1 mRNA dropped to about 25% of the reference value within four generations (after about 8-10 weeks of culture). In one case, NHBEC subpassages were followed over a period of 20 weeks. In this system MRP mRNA levels increased by more than threefold, while levels of MRP1 protein and LRP mRNA and protein were expressed at almost constant rates.

The transport of molecules across membranes is an essential function of all living organisms and a large number of specific transporters have evolved to carry out this function. The largest transporter gene family is the ATP-binding cassette (ABC) transporter superfamily. The multidrug resistance-associated protein (MRP) family is comprised of nine related ABC transporters. The intra-cellular distribution of the different MRP isoforms in relation to their physiological and non physiological function is still a point of discussion. For this purpose we used normal human lung cells (bronchial epithelial cells, NHBEC, and peripheral lung cells, PLC) as well as tumor cell cultures as test tools to investigate the intracelluar localization of these proteins under classical culture conditions and under air-liquid interface by means of indirect fluorescence microscopy. Characterization of the cultured cells as lung epithelial cells was performed by means of immuno-histochemical analysis. MRP1 and MRP3 were localised to the cellular membrane in all tested lung cell types. In contrast to that MRP2, MRP4 and MRP5 could be described as intracellular proteins in NHBEC and PLC. All MRP1-MRP5 isoforms could be characterized in A549 tumor cell line as membrane proteins. In order to imitate the physiological in vivo circumstances in the lung, we have established a dry/wet method (air-liquid interface) for cell cultivation so that cultured cells have the option to polarize between air and basal membrane and this might influence the distribution pattern of MRP1 and MRP2 in NHBEC. Using confocal laser scanning techniques we could show that in cells kept under dry/wet conditions MRP1 was found to be localised to baso-lateral cell regions while MRP2 was localised to all cell regions. Under classical culture conditions MRP1 was not localized to particular membrane regions and MRP2 was found to be an intracellular protein.

This paper shows how to estimate the likely death and sickness rates caused by release of toxic material when the probability of a spill, the amount spilled, the amount transported by air or water away from the primary spill site, and the types of material spilled have uncertainties. In addition, using risk methods that include quantitative procedures for determining the relative contribution, relative importance, and relative sensitivity of the uncertainties, which of the uncertain parameters is causing the greatest degree of uncertainty in the death and sickness rates, can also be identified. This affords the reduction of uncertainty. In this way, focusing on limiting the parameters that are dominant without spending effort and money on parameters that contribute little to lessening of uncertainty of death and sickness rates is possible. In addition, synergistic effects are considered for two toxic materials combining to produce either a more virulent or benign toxic effect than the original materials. For such synergistic involvement, death and sickness rates are also quantitatively described with the dominance ordering of uncertain parameters involved in the synergism. The numerical illustrations exemplify the method for assessing the risk and uncertainty and also illustrate the use of uncertainty to more precisely determine what is necessary to ameliorate the risk to the maximum extent possible.

Likely death and sickness rates caused by a toxic contaminant release with a resistance to sickness that is age dependent are explored. As many as 10 different sicknesses can be allowed for each released contaminant. Transport of portions of released contaminant by airborne or waterborne methods leads to different contaminant levels and therefore, different death and sickness rates. Gender-specific sicknesses (e.g., prostate cancer or ovarian cancer) can also be included, allowing broad usage of the quantitative procedure described. The influence of uncertainty in parameters relating to either the age dependence model for sickness or death rates, the age distribution model of the population, or the spill and transport of toxic contaminant can easily be handled using a risking program such as Crystal Ball, in conjunction with the basic death and sickness rate program. Several numerical illustrations show how to assess likely death and sickness rates under these influences.

The expression of MDR1b coding mRNA is increased in alveolar type II cells from juvenile rat lung in culture. Hydrogen peroxide and paraquat-induced further upregulation supporting that oxidative stress mediated mechanisms are involved in the regulation of MDR1b in rat lung. The expression rates of mRNA for catalase, Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and Mn-superoxide dismutase (Mn-SOD) remains constant during culture and were not modulated by hydrogen peroxide or paraquat. Thus, antioxidative enzymes in primary A II cells from rat lung are not regulated by reactive oxygen species dependent mechanisms. Primary A II cells were substantially more sensitive towards paraquat-induced cytotoxicity and lipid peroxidation than the permanent human lung tumor cell lines H322 and H358. A 100 microM hydrogen peroxide for 2h induces substantial DNA damage which is not paralleled by an increased rate of lipid peroxidation. The expression rate of mRNA coding for catalase and Mn-SOD was not changed and almost the same is true for the activity of catalase and Cu/Zn-SOD. Only 50 microM paraquat induced a significant decrease in catalase activity and an increase in Cu/Zn-SOD activity.

Nanotechnology offers enormous potential for technological progress. Fortunately, early and intensive efforts have been invested in investigating toxicology and safety aspects of this new technology. However, despite there being more than 6,000 publications on nanotoxicology, some key questions still have to be answered and paradigms need to be challenged. Here, we present a view on the field of nanotoxicology to stimulate the discussion on major knowledge gaps and the critical appraisal of concepts or dogma. First, in the ongoing debate as to whether nanoparticles may harbour a specific toxicity due to their size, we support the view that there is at present no evidence of ‘nanospecific’ mechanisms of action; no step-change in hazard was observed so far for particles below 100 nm in one dimension. Therefore, it seems unjustified to consider all consumer products containing nanoparticles a priori as hazardous. Second, there is no evidence so far that fundamentally different biokinetics of nanoparticles would trigger toxicity. However, data are sparse whether nanoparticles may accumulate to an extent high enough to cause chronic adverse effects. To facilitate hazard assessment, we propose to group nanomaterials into three categories according to the route of exposure and mode of action, respectively: Category 1 comprises nanomaterials for which toxicity is mediated by the specific chemical properties of its components, such as released ions or functional groups on the surface. Nanomaterials belonging to this category have to be evaluated on a case-by-case basis, depending on their chemical identity. Category 2 focuses on rigid biopersistent respirable fibrous nanomaterials with a specific geometry and high aspect ratio (so-called WHO fibres). For these fibres, hazard assessment can be based on the experiences with asbestos. Category 3 focuses on respirable granular biodurable particles (GBP) which, after inhalation, may cause inflammation and secondary mutagenicity that may finally lead to lung cancer. After intravenous, oral or dermal exposure, nanoscaled GBPs investigated apparently did not show ‘nanospecific’ effects so far. Hazard assessment of GBPs may be based on the knowledge available for granular particles. In conclusion, we believe the proposed categorization system will facilitate future hazard assessments.

Multidrug resistance type 1 P-glycoproteins (P-gp) and multidrug resistance associated proteins (MRP) were studied in differentiated primary human lung cells in culture, in comparison with permanent human lung cell lines and primary alveolar type II cells from rat lung. AII cells exhibited low basal levels of mdr1b mRNA, that increased over time and after oxygen radical production induced by paraquat. mRNAs coding for antioxidative enzymes catalase (CAT), maganese superoxide dismutase (Mn-SOD) and copper/zinc superoxide dismutase (Cu/Zn-SOD) were not changed. H358, A549, H322 cells expressed low levels of MDR1 mRNA, but the mdr1 substrate rhodamine 123 (Rh 123) was transported out of H358 and H322 cells in a non-invasive, single cell fluorescence assay. The dye efflux could be inhibited by the chemosensitizer, verapamil. Normal human bronchial epithelial cells (NHBEC) expressed immuno-reactive MDR1 P-gp and the MPR protein that was active in the fluorescence assay using the MRP substrate carboxy-dichlorofluorescein (CDF) and MK-571 as an inhibitor. We did observe inter-individual variation of MRP in both the mRNA and the immunoreactive protein in NHBEC culture. Over time (12 weeks) the protein was relatively stable in NHBEC and epithelial cells from peripheral lung (PLC), but the mRNA level was drastically increased when explant cultures were continued (18 weeks).

The mutant frequency (MF) in the hypoxanthine-guanine-phosphoribosyl-transferase (HPRT) locus of peripheral blood T-lymphocytes was measured in a population environmentally exposed to vinyl chloride - a toxic and carcinogenic substance through an accidental release into the atmosphere. It was compared to MF in a control group of unexposed individuals. Both groups were re-investigated in a follow-up study, 2 years later. No significant difference could be observed in MF between exposed and controls either at the accident nor in the follow-up study. Approximately the same mean HPRT mutant frequencies were observed for both groups in T-lymphocytes from blood samples obtained shortly after the accident and from the follow-up blood samples. Both groups showed a higher mean MF in the re-investigation samples which is most probably due to the significantly lower average cloning efficiency (CE) under non-selective conditions and because of the inverse relationship between CE and MF. The exposed population showed a higher mean T-cell CE at the initial blood sampling as compared to the control group. The concurrent cytogenetic analyses of peripheral lymphocytes showed a significant increase in cells with aberrations in the exposed population. Clastogenic but not mutagenic activity of vinyl chloride was observed in our study.

Objectives: Applications of OMICS to high throughput studies of changes of genes, RNAs, proteins, metabolites, and their associated functions in cells or organisms exposed to environmental chemicals has led to the emergence of a very active research field: environmental OMICS. This developing field holds an important key for improving the scientific basis for understanding the potential impacts of environmental chemicals on both health and the environment. Here we describe the state of environmental OMICS with an emphasis on its recent accomplishments and its problems and potential solutions to facilitate the incorporation of OMICS into mainstream environmental and health research. Data sources: We reviewed relevant and recently published studies on the applicability and usefulness of OMICS technologies to the identification of toxicity pathways, mechanisms, and biomarkers of environmental chemicals for environmental and health risk monitoring and assessment, including recent presentations and discussions on these issues at The First International Conference on Environmental OMICS (ICEO), held in Guangzhou, China during November 8-12, 2011. This paper summarizes our review. Synthesis: Environmental OMICS aims to take advantage of powerful genomics, transcriptomics, proteomics, and metabolomics tools to identify novel toxicity pathways/signatures/biomarkers so as to better understand toxicity mechanisms/modes of action, to identify/categorize/prioritize/screen environmental chemicals, and to monitor and predict the risks associated with exposure to environmental chemicals on human health and the environment. To improve the field, some lessons learned from previous studies need to be summarized, a research agenda and guidelines for future studies need to be established, and a focus for the field needs to be developed. Conclusions: OMICS technologies for identification of RNA, protein, and metabolic profiles and endpoints have already significantly improved our understanding of how environmental chemicals affect our ecosystem and human health. OMICS breakthroughs are empowering the fields of environmental toxicology, chemical toxicity characterization, and health risk assessment. However, environmental OMICS is still in the data generation and collection stage. Important data gaps in linking and/or integrating toxicity data with OMICS endpoints/profiles need to be filled to enable understanding of the potential impacts of chemicals on human health and the environment. It is expected that future environmental OMICS will focus more on real environmental issues and challenges such as the characterization of chemical mixture toxicity, the identification of environmental and health biomarkers, and the development of innovative environmental OMICS approaches and assays. These innovative approaches and assays will inform chemical toxicity testing and prediction, ecological and health risk monitoring and assessment, and natural resource utilization in ways that maintain human health and protects the environment in a sustainable manner.

Long-term cultures of human hepatocytes were maintained serum-free in a chemically defined medium in the presence of HGF and EGF for up to 30 days. STAT 1alpha/1beta, STAT 3, and STAT 5 were present and tyrosine phosphorylated throughout the culture period in the cytosol as well as the nucleus. We show by co-immunoprecipitation that a portion of the cellular pools of STAT 1alpha/1beta and STAT 5 is physically associated with c-MET and EGF-receptor. Co-immunoprecipitation of STAT 3 with STAT 5 did occur in the cytosol but not in the nucleus, suggesting dimerization of the two STAT family members. The observed differences of protein amounts and tyrosine phosphorylation between cytosol and nucleus, the association of STAT proteins with EGF-receptor and c-MET and with each other may all be involved in regulating the activity of the STAT transcription factors. It is intriguing to speculate that STAT 5 may have a modulating role in the regulation of STAT 3 activity.

Mammalian liver exhibits expression of members of the family of multidrug resistance (mdr) transporters (P-glycoproteins). P-glycoprotein isoforms encoded by mdr1 genes participate in extrusion of an array of xenobiotics into the bile. Induction of mdr1b mRNA expression has been shown to occur in rat hepatocytes in response to hepatotrophic growth factors. As the cytokine tumor necrosis factor alpha (TNF-alpha) is known to exert a direct mitogenic effect on hepatocytes, its influence on mdr1b expression was investigated. In primary rat hepatocytes cultured in the absence of TNF-alpha, a time-dependent increase in basal expression of mdr1b mRNA and in immunodetectable P-glycoprotein was observed. In cells treated with TNF-alpha (4,000 U/ml) for 3 days, expression of mdr1b mRNA and of immunodetectable P-glycoprotein was induced approximately twofold. Moreover, intracellular steady-state levels of the mdr1 substrate rhodamine 123 were decreased in cells pretreated with TNF-alpha in comparison to controls, indicating an increase in functional transporter(s) mediating dye extrusion. Treatment of hepatocytes with antioxidants (1 mM ascorbic acid and 2% dimethyl sulfoxide) for 3 days markedly suppressed mdr1b mRNA and P-glycoprotein expression both in cells cultured in the presence of TNF-alpha and in the absence of the cytokine, but did not fully abolish mdr1b mRNA induction by TNF-alpha, supporting the notion that reactive oxygen species participate in regulation of basal mdr1b gene expression during hepatocyte culture. In conclusion, the present data indicate that by inducing mdr1b expression in hepatocytes, TNF-alpha may affect the capacity of the liver for extrusion or detoxification of endogenous or xenobiotic mdr1 substrates.

The scope of the present study was to investigate whether nicotine or cotinine will affect the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in isolated perfused rat lungs and livers and to study the effect of starvation on pulmonary metabolism of NNK. NNK metabolism was investigated in isolated perfused liver and lung of male F344 rats perfused with 35 nM [5-3H]NNK in presence of a 1400-fold excess of the main tobacco alkaloid nicotine and its metabolite cotinine. In perfused rat livers, nicotine and cotinine inhibited NNK elimination and metabolism and led to a substantial increase of elimination half-life from 14.6 min in controls to 25.5 min after nicotine and 36.6 min after cotinine co-administration, respectively. In parallel, the pattern of NNK metabolites was changed by nicotine and cotinine. The pathway of alpha-hydroxylation representing the metabolic activation of NNK was decreased to 77% and 85% of control values, whereas N-oxidation of NNK and glucuronidation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) was increased 2.6- and 1.2-fold in presence of nicotine and cotinine, respectively. When isolated rat lungs were perfused with 35 nM NNK for 3 h neither the elimination nor the pattern of metabolites were substantially affected due to co-administration of 50 microM nicotine or cotinine. Cytochrome P450 2E1 is known to participate in the activation of NNK and can be induced by starvation. However, isolated rat lungs from male Sprague Dawley rats perfused with [1-14C]NNK at about 2 microM for 3 h, revealed only small differences in pulmonary elimination and pattern of NNK metabolites between fed and starved animals. These results suggest that nicotine and its main metabolite cotinine inhibit the metabolic activation of NNK predominantly in the liver whereas activation in lung, a main target organ of NNK induced carcinogenesis, remained almost unaffected.

Germany's energy supply system needs to face a transition with a view to achieve an energy supply that is economically sustainable, reliable, and climate-friendly by 2050. The political hurdles for transitioning to a wholly renewable electricity supply with a strong European perspective, are discussed in this chapter. These include: the new EU energy and environmental policy competency framework pursuant to the Lisbon Treaty; the future of EU climate and energy policy; bilateral and multilateral cooperation; and the policy conditions needed nationally for transition to a wholly renewable electricity supply. Energy efficiency is a key precondition for transitioning to an affordable renewable electricity supply. The regulatory aspects need to address how an optimized electricity transmission grid planning process can be achieved and which economic incentives for electricity storage facility and grid expansion are needed as support. Keywords:Germany's energy supply; renewable electricity; renewable energy act (EEG)

Proteomics is the large-scale study of gene expression at the protein level. This cutting edge technology has been extensively applied to toxicology research recently. The up-to-date development of proteomics has presented the toxicology community with an unprecedented opportunity to reexamine conventional toxicological principles, methods and practices, and to transform this traditional subject into more informative and comprehensive science for a better understanding of the potential toxic mechanisms and/or modes of action, toxicity pathways, environmental biomarkers, and assessment of adverse human health risks. The application of proteomics and other OMICS technologies to toxicology has given rise to the new field of toxicology, systems toxicology. This book chapter provides an introduction to modern proteomic technologies and approaches, with particular reference to their applications to toxicology. Key proteomic technologies such as two-dimensional gel electrophoresis based and mass spectrometry-based proteomic methods and approaches are described. Examples of recent applications of these technologies and methodologies to mechanistic toxicology and applied toxicology such as chemical toxicity testing and screening, clinical toxicology, drug discovery, environmental toxicity, and toxicity biomarker are presented. The discussion includes a focus on challenges and future directions of toxicoproteomics and systems toxicology. Keywords: proteomics; toxicology; toxicity pathways; protein expression; protein post-translational modification; protein biomarker; systems toxicology

Despite the fact that more than 5000 safety-related studies have been published on bisphenol A (BPA), there seems to be no resolution of the apparently deadlocked controversy as to whether exposure of the general population to BPA causes adverse effects due to its estrogenicity. Therefore, the Advisory Committee of the German Society of Toxicology reviewed the background and cutting-edge topics of this BPA controversy. The current tolerable daily intake value (TDI) of 0.05 mg/kg body weight [bw]/day, derived by the European Food Safety Authority (EFSA), is mainly based on body weight changes in two- and three-generation studies in mice and rats. Recently, these studies and the derivation of the TDI have been criticized. After having carefully considered all arguments, the Committee had to conclude that the criticism was scientifically not justified; moreover, recently published additional data further support the reliability of the two- and three-generation studies demonstrating a lack of estrogen-dependent effects at and below doses on which the current TDI is based. A frequently discussed topic is whether doses below 5 mg/kg bw/day may cause adverse health effects in laboratory animals. Meanwhile, it has become clear that positive results from some explorative studies have not been confirmed in subsequent studies with higher numbers of animals or a priori defined hypotheses. Particularly relevant are some recent studies with negative outcomes that addressed effects of BPA on the brain, behavior, and the prostate in rodents for extrapolation to the human situation. The Committee came to the conclusion that rodent data can well be used as a basis for human risk evaluation. Currently published conjectures that rats are insensitive to estrogens compared to humans can be refuted. Data from toxicokinetics studies show that the half-life of BPA in adult human subjects is less than 2 hours and BPA is completely recovered in urine as BPA-conjugates. Tissue deconjugation of BPA-glucuronide and -sulfate may occur. Because of the extremely low quantities, it is only of minor relevance for BPA toxicity. Biomonitoring studies have been used to estimate human BPA exposure and show that the daily intake of BPA is far below the TDI for the general population. Further topics addressed in this article include reasons why some studies on BPA are not reproducible; the relevance of oral versus non-oral exposure routes; the degree to which newborns are at higher systemic BPA exposure; increased BPA exposure by infusions in intensive care units; mechanisms of action other than estrogen receptor activation; and the current regulatory status in Europe, as well as in the USA, Canada, Japan, New Zealand, and Australia. Overall, the Committee concluded that the current TDI for BPA is adequately justified and that the available evidence indicates that BPA exposure represents no noteworthy risk to the health of the human population, including newborns and babies.

Embryonen und Feten konnen eine eigene Sensitivitat gegenuber Arzneimittelwirkungen haben, die sich nur zu bestimmten Entwicklungsstufen wahrend der Schwangerschaft auspragt. Daher konnen Arzneimittelbedingte pranatal-toxische Wirkungen unterschiedliche Phasen der Entwicklung betreffen.

Under the new European chemical legislation REACH (EG 1907/2006), dangerous properties of chemical substances will be evaluated and data gaps will be closed. This information is needed for other regulations, such as safety at the working place or for the safe handling of products. Existing knowledge on chemical compounds must be broadened because previous regulations have focused on high production volume compounds. The evaluation procedures needed too much time, and for the majority of non-evaluated substances a new strategy is needed. REACH places the duty for registration of substances with the producers and importers. Data gaps for risk evaluation will be closed. Competent authorities will be relieved from the primary risk evaluation of most substances. Alternative strategies of evaluation using previous information and non-animal testing approaches will be supported to avoid animal testing where appropriate. The new European chemical agency ECHA will use the provided information in order to identify very dangerous chemical substances which should be controlled by authorization of its use and the circumstances thereof.

Workers occupationally exposed to cadmium, cobalt and lead have been reported to have increased levels of DNA damage. To analyze whether in vivo relevant concentrations of heavy metals cause systematic alterations in RNA expression patterns, we performed a gene array study using primary normal human bronchial epithelial cells. Cells were incubated with 15 microg/l Cd(II), 25 microg/l Co(II) and 550 microg/l Pb(II) either with individual substances or in combination. Differentially expressed genes were filtered out and used to identify enriched GO categories as well as KEGG pathways and to identify transcription factors whose binding sites are enriched in a given set of promoters. Interestingly, combined exposure to Cd(II), Co(II) and Pb(II) caused a coordinated response of at least seven stress response-related transcription factors, namely Oct-1, HIC1, TGIF, CREB, ATF4, SRF and YY1. A stress response was further corroborated by up regulation of genes involved in glutathione metabolism. A second major response to heavy metal exposure was deregulation of the cell cycle as evidenced by down regulation of the transcription factors ELK-1 and the Ets transcription factor GABP, as well as deregulation of genes involved in purine and pyrimidine metabolism. A third and surprising response was up regulation of genes involved in steroid metabolism, whereby promoter analysis identified up regulation of SRY that is known to play a role in sex determination. A forth response was up regulation of xenobiotic metabolising enzymes, particularly of dihydrodiol dehydrogenases 1 and 2 (AKR1C1, AKR1C2). Incubations with individual heavy metals showed that the response of AKR1C1 and AKR1C2 was predominantly caused by lead. In conclusion, we have shown that in vivo relevant concentrations of Cd(II), Co(II) and Pb(II) cause a complex and coordinated response in normal human bronchial epithelial cells. This study gives an overview of the most responsive genes.

During the last two decades, substantial efforts have been made towards the development and international acceptance of alternative methods to safety studies using laboratory animals. In the EU, challenging timelines for phasing out of many standard tests using laboratory animals were established in the seventh Amending Directive 2003/15/EC to Cosmetics Directive 76/768/EEC. In continuation of this policy, the new European Chemicals Legislation (REACH) favours alternative methods to conventional in vivo testing, if validated and appropriate. Even alternative methods in the status of prevalidation or validation, but without scientific or regulatory acceptance may be used under certain conditions. Considerable progress in the establishment of alternative methods has been made in some fields, in particular with respect to methods predicting local toxic effects and genotoxicity. In more complex important fields of safety and risk assessment such as systemic single and repeated dose toxicity, toxicokinetics, sensitisation, reproductive toxicity and carcinogenicity, it is expected that the development and validation of in silico methods, testing batteries (in vitro and in silico) and tiered testing systems will have to overcome many scientific and regulatory obstacles which makes it extremely difficult to predict the outcome and the time needed. The main reasons are the complexity and limited knowledge of the biological processes involved on one hand and the long time frame until validation and regulatory acceptance of an alternative method on the other. New approaches in safety testing and evaluation using “Integrated Testing Strategies” (ITS) (including combinations of existing data, the use of chemical categories/grouping, in vitro tests and QSAR) that have not been validated or not gained wide acceptance in the scientific community and by regulatory authorities will need a thorough justification of their appropriateness for a given purpose. This requires the availability of knowledge and experience of experts in toxicology. The challenging deadlines for phasing out of in vivo tests in the Cosmetics Amending Directive 2003/15/EC appear unrealistic. Likewise, we expect that the application of validated alternative methods will only have a small or moderate impact on the reduction of in vivo tests under the regimen of REACH, provided that at least the same level of protection of human health as in the past is envisaged. As a consequence, under safety aspects, it appears wise to consider established in vivo tests to be indispensable as basic tools for hazard and risk assessment with respect to systemic single and repeated dose toxicity, sensitisation, carcinogenicity and reproductive toxicity, especially regarding quantitative aspects of risk assessment such as NOAELs, LOAELs and health-related limit values derived from them. Based on the overall evaluation in this review, the authors are of the opinion that in the short- and mid-term, the strategy of the development of alternative methods should be more directed towards the refinement or reduction of in vivo tests. The lessons learnt during these efforts will provide a substantial contribution towards the replacement initiatives in the long-term.

Primary cultures of human lung cells can serve as a model system to study the mechanisms underlying the effects of irritants in air and to get a deeper insight into the (patho)physiological roles of the xenobiotic detoxification systems. For 99 human lung cancer cases the culture duration for bronchial epithelium and peripheral lung cells (PLC) are given in term of generations and weeks. Using this system, we investigated whether and how prostaglandins (PG) modify multidrug resistance related protein (MRP) function in normal human lung cells. PGF2alpha had no effect on MRP function, whereas PGE2 induced MRP activity in cultured NHBECs. The transport activity study of MRP in NHBEC, PLC, and A549 under the effect of exogenously supplied PGF2alpha (10 microM, 1 day) using single cell fluorimetry revealed no alteration in transport activity of MRP. PG concentrations were within the physiological range. COX I and II inhibitors indomethacin (5, 10 microM) and celecoxib (5, 10 microM) could substantially decrease the transport activity of MRP in NHBEC, PLC, and A549 in 1- and 4-day trials. Prostaglandin E2 did not change cadmium-induced caspase 3/7 activation in NHBECs and had no own effect on caspase 3/7 activity. Cadmium chloride (5, 10 microM) was an effective inducer of caspase 3/7 activation in NHBECs with a fivefold and ninefold rise of activity. In primary human lung cells arachidonic acid activates MRP transport function only in primary epithelial lung cells by prostaglandin E2 but not by F2alpha mediated pathways and this effect needs some time to develop.

J. G. Hengstler*, H. Foth, R. Kahl, P.J. Kramer, W. Lilienblum, T. Schulz, H. Schweinfurth Center for Toxicology, University of Leipzig, Institute of Legal Medicine and Rudolf Boehm Institute of Pharmacology and Toxicology, Haertelstr 16-18, 04107 Leipzig, Germany Institute of Environmental Toxicology, University of Halle, D-06097 Halle/Saale, Germany Institute of Toxicology, Heinrich-Heine-University, PO Box 101007, 40001 Dusseldorf, Germany Institute of Toxicology, Merck KGaA, 64271 Darmstadt, Germany Consultant of Toxicology, Lindenweg 15, D-30966 Hemmingen/Han, Germany Thomas Schulz Bundesinstitut fur Risikobewertung (BfR), Thielallee 88-92, 14195 Berlin, Germany Experimental Toxicology, Schering AG, 13342 Berlin, Germany

The existing systems of classification of carcinogens should include a distinction between genotoxic and non-genotoxic chemicals. For non-genotoxic chemicals, permissible exposure levels can be derived at which no relevant human cancer risks are anticipated. While genotoxic carcinogens can induce chromosomal effects without mutagenic action, non-DNA-reactive genotoxins affecting topoisomerase or the spindle, or those having an exclusively aneugenic effect can be carcinogenic only at high, toxic doses. Specific mechanisms of clastogenicity and processes of carcinogenesis based on reactive oxygen have practical thresholds. Since reactive oxygen species (ROS) are generally genotoxic, the question is whether chemicals that increase ROS production will add to endogenously produced background levels and lead to nonlinear dose-effect relationships. Taking into account the presence of endogenous carcinogens, it is now becoming evident that carcinogenic risk extrapolation to low doses must be considered according to the mode of action.

The existing systems of classification of carcinogens should include a distinction between genotoxic and non-genotoxic chemicals. For non-genotoxic chemicals, permissible exposure levels can be derived at which no relevant human cancer risks are anticipated. While genotoxic carcinogens can induce chromosomal effects without mutagenic action, non-DNA-reactive genotoxins affecting topoisomerase or the spindle, or those having an exclusively aneugenic effect can be carcinogenic only at high, toxic doses. Specific mechanisms of clastogenicity and processes of carcinogenesis based on reactive oxygen have practical thresholds. Since reactive oxygen species (ROS) are generally genotoxic, the question is whether chemicals that increase ROS production will add to endogenously produced background levels and lead to nonlinear dose-effect relationships. Taking into account the presence of endogenous carcinogens, it is now becoming evident that carcinogenic risk extrapolation to low doses must be considered according to the mode of action., U postojećem sistemu klasifikacije kancerogenih tvari utvrđena je razlika između genotoksičnih i negenotoksičnih kemikalija. Za negenotoksične kemikallije mogu se izvesti pretpostavljeni stupnjevi izlaganja kod kojih ne postoji značajan rizik od pojave raka kod ljudi. Za genotoksične kancerogene mogući su na primjer inducirani kromosomski efekti bez početka procesa mutageneze, dok genotoksični toksini koji se ne vežu za DNA-molekulu, a djeluju na topoizomere ili diobeno vreteno ili su aneugeni, izazivaju kancerogene efekte jedino u visokim, toksičnim dozama. Za specifične mehanizme klastrogenog djelovanja i procesa kancerogeneze koji se baziraju na reaktivnom kisiku postoji prag početka procesa. Kako su vrste kemikalija reaktivne na kisik (ROS) u načelu genotoksične, pojavljuju se pitanja da li kemikalije koje povećavaju produkciju ROS-vrsta treba pridodati endogenim kancerogenima pozadinskog stupnja koji uzrokuju nelinearni odnos doze i učinka. Uzimajući u obzir rasprave o prisutnosti endogenih kancerogena, sada postaje jasno da se kancerogeni rizik od niskih doza mora uzeti u obzir sukladno načinu njihova djelovanja.

Existing systems of classification of carcinogens are a matter of discussion, world-wide. There is agreement that it should be distinguished between genotoxic and non-genotoxic chemicals. The risk assessment approach used for non-genotoxic chemicals is similar among different regulatory bodies: insertion of an uncertainty (safety) factor permits the derivation of permissible exposure levels at which no relevant human cancer risks are anticipated. For genotoxic carcinogens, case studies of chemicals point to a whole array of possibilities. Positive data of chromosomal effects only, in the absence of mutagenicity, may support the characterization of a compound that produces carcinogenic effects only at high, toxic doses. Non-DNA-reactive genotoxins, such as topoisomerase inhibitors or inhibitors of the spindle apparatus are considered in this respect. In such cases, arguments are in favour of the existence of "practical" thresholds. Taking existing concepts together, it is proposed to basically distinguish between "perfect" and "practical" thresholds. There is a wide consensus that for non-DNA-reactive genotoxins such as aneugens (aneuploidy, chromosome loss, non-disjunction) thresholds should be defined. It is being discussed as to whether the identification of possible threshold effects should also include other mechanisms of genotoxicity, in addition to aneugenic effects. Specific mechanisms of clastogenicity have been repeatedly addressed as also having thresholds, such as topoisomerase II poisons or mechanisms based on reactive oxygen. Oxidative stress as an important mechanism is triggered by exposure to exogenous factors such as ultraviolet (UV) and ionizing radiation, anoxia and hyperoxia, and by chemicals producing reactive oxygen species. The idea is receiving increased support that reactive oxygen species (ROS)-mediated processes of carcinogenesis have practical thresholds. Since reactive oxygen species are genotoxic in principle, questions arise whether chemicals that increase ROS production will superimpose to an endogenously produced background level of DNA lesions, related to mechanisms that may result in non-linear dose-effect relationships. The existence of "endogenous" DNA adducts has been generally accepted, and possible regulatory implications of the presence of endogenous carcinogens have been discussed. It is now becoming evident that a diversity of methods of carcinogenic risk extrapolation to low doses must be considered, dependent on the mode of action. Although there is an increasing international awareness of these developments, the system of classification of carcinogens of the European Union still remains static. This should be changed, as the philosophy of separation of a strictly sequential "hazard assessment" and "risk assessment" appears out-of-date.

Nanotechnology represents one of the key technologies of the twenty-first century and includes all methods that allow production, and analysis of objects sized between one and 100 nm. A large number of nanomaterials and consumer products are already used, such as paints, car tyres, tennis rackets, textiles and sunscreens. Technologically more important than use of nanomaterials in consumer products are applications in electronics, construction materials or coatings. It is expected moreover that in some areas, nanotechnologies will bring large social benefits, as with pharmaceuticals, medical technology and water purification. There are also hopes that nanotechnologies will make an important contribution to protecting the environment. While great expectations are placed in the potential of nanotechnologies, there are also increasing warnings of possible risks due to insufficient knowledge about the effects of these technologies on the human organism and the environment (SRU 2011a). Available knowledge on the risks of nanoparticles and nanofibres varies in extent, and in many cases, notably regarding exposures, there are major gaps in that knowledge. In recent years, the number of contributions about nanotechnology submitted to our journal has massively increased (Gibson et al. 2011; Truong et al. 2011; Heng et al. 2011a; Jeong et al. 2010). Cutting-edge topics in our journal are uptake and biodistribution (Zhang et al. 2011; Gehrke et al. 2011; Xie et al. 2010), inflammation and apoptosis (Heng et al. 2011b; Lee et al. 2011; Marano et al. 2011) as well as oxidative stress and genotoxicity (Foldbjerg et al. 2011; Clift et al. 2011; Kim et al. 2011) induced by nanoparticles. From the research findings to date, there is no proof of adverse changes in the environment or in human health as a result of the manufacture and use of nanoparticles and nanofibres currently on the market. This cannot be taken as an all-clear, however, because understanding of the risks of these materials remains very incomplete and some research findings raise substantial concerns. A distinction can be made between materials that have been on the market for some time, where there are already toxicology and exposure studies, and new materials where hardly anything is known about toxicological profiles and environmental fate. Public debate about the opportunities and risks of nanotechnology has started (SRU 2011b) and need to be addressed by toxicologist. There are already initial efforts at classifying nanoparticles and nanofibres into risk categories. Such materials should nonetheless be subjected case by case to sciencebased risk assessment for time being, as too much information on risk-determining characteristics is lacking and even very small differences, such as a coating, can critically alter a material’s effects in biological systems. A crucial property for science-based risk assessment is the ability of nanoparticles and nanofibres to reach parts of organisms and cells where comparable materials at a larger H. Foth (&) Martin-Luther-Universitat Halle-Wittenberg, Franzosenweg 1 a, 06097 Halle (Saale), Germany e-mail: heidi.foth@medizin.uni-halle.de