Search

Information on the kinetic characteristics of soil enzymes under long-term arsenic (As) pollution in field soils is scarce. We investigated Michaelis-Menten kinetic properties of four soil enzymes including β-glucosidase (BG), acid phosphatase (ACP), alkaline phosphatase (ALP), and dehydrogenase (DHA) in field soils contaminated by As resulting from long-term realgar mining activity. The kinetic parameters, namely the maximum reaction velocity (V max ), enzyme-substrate affinity (K m ) and catalytic efficiency (V max /K m ) were calculated. Results revealed that the enzyme kinetic characteristics varied in soils and were significantly influenced by total nitrogen (N) and total As, which explained 31.8% and 30.7% of the variance in enzyme kinetics respectively. Enzyme pools (V max ) and catalytic efficiency (V max /K m ) of BG, ACP and DHA decreased with elevated As pollution, while the enzyme affinity for substrate (K m ) was less affected. Redundancy analysis and stepwise regression suggested that the adverse influence of As on enzyme kinetics may offset or weakened by soil total N and soil organic matter (SOM). Concentration-response fitting revealed that the specific kinetic parameters expressed as the absolute enzyme kinetic parameters multiplied by normalized soil total N and SOM were more relevant than the absolute ones to soil total As. The arsenic ecological dose values that cause 10% decrease (ED 10 ) in the specific enzyme kinetics were 20-49 mg kg -1 , with a mean value of 35 mg kg -1 , indicating a practical range of threshold for As contamination at field level. This study concluded that soil enzymes exhibited functional adaptation to long-term As stress mainly through the reduction of enzyme pools (Vmax) or maintenance of enzyme-substrate affinity (K m ). Further, this study demonstrates that the specific enzyme kinetics are the better indicators of As ecotoxicity at field-scale compared with the absolute enzyme parameters., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The toxicity of heavy metals (HMs) to soil enzymes is directly influenced by the status of the enzyme (free vs. immobilized on minerals) and the duration of exposure. However, little information is available on the interaction effect of HMs, mineral, and exposure time on soil enzyme activities. We investigated the interaction mechanism of alkaline phosphatase (ALP) with minerals (montmorillonite and goethite) and the response of free and immobilized ALP to cadmium (Cd) toxicity under different exposure times. The adsorption isotherms of ALP on both minerals were L-type. The maximum adsorption capacity of goethite for ALP was 3.96 times than montmorillonite, although both had similar adsorption constant (K). Goethite showed a greater inhibitory effect on ALP activity than montmorillonite. The toxicity of Cd to free- and goethite-ALP was enhanced with increasing exposure time, indicating a time-dependent inhibition. However, Cd toxicity to montmorillonite-ALP was not affected by the exposure time. The inhibition of Cd to soil enzyme activity is influenced by the properties of mineral complexes and the duration of exposure. A further understanding of the time pattern of HMs toxicity is helpful for accurately assessing the hazards of HMs to soil enzyme activity., (Copyright © 2018 Elsevier Inc. All rights reserved.)

In the ecotoxicological assessment of petroleum hydrocarbon-contaminated soil, microbial community profile is important aspect due to their involvement in soil functions. However, soil physicochemical properties and the inhabiting plants could dictate the microbial composition. A question remains unanswered is, how an integrated approach may be utilized to account for various contrasting soil properties, plant types (reference vs. native) and the nature of the hydrocarbon contamination. In this study, we utilized bacterial DNA profiling techniques to investigate the relationship between soil properties, contaminant and plant species. Results identified that Proteobacteria and Actinobacteria were the most abundant bacteria of the 45 phyla identified in the hydrocarbon-contaminated soil. The bulk and rhizosphere microbiome showed that the contaminated soil originally had quite distinct bacterial communities compared to the artificially contaminated soil (mine soil = 95 genera vs. other soils = 2-29 genera). In these cases, not significantly but the native plant slightly increased bacterial diversity and relative abundance in the same soils. Also, within each site, the bacterial community was significantly altered with the hydrocarbon concentration. In this instance, the influence of the contaminant was strong and also with the soil pH and organic matter. These results would significantly contribute to the novel insights on the molecular technique-based hydrocarbon toxicity assessment and the development of the further integrative approach with other microbial community and their metabolic profile in the contaminated sites., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Arsenic (As) and copper (Cu) are co-contaminants in the environment but little is known about their ecological impact as mixtures in soil. In this study, we investigated the combined As-Cu interactions on toxicity and uptake as binary mixtures in 5 contrasting soils. The study included solubility, contaminant uptake and toxicity in cucumber (Cucumis sativus L.) as a model plant species. Soils were spiked individually and as a mixtures at 10 different As levels (2, 4, 8 up to 1024mgkg -1 ). Copper was added with As at two effective concentration levels (EC10 Cu and EC50 Cu ). Arsenic uptake was significantly reduced in the presence of Cu and a higher effect was demonstrated with increasing pore-water pH. Copper accumulation was not significantly influenced by As. An additive response on plant growth was predominant overall when expressed from pore-water parameters with root mean square errors of 12.6 and 13.2 for EC10 Cu and EC50 Cu treatments, respectively., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Arsenic (As) is an inhibitor of phosphatase, however, in the complex soil system, the substrate concentration effect and the mechanism of As inhibition of soil alkaline phosphatase (ALP) and its kinetics has not been adequately studied. In this work, we investigated soil ALP activity in response to As pollution at different substrate concentrations in various types of soils and explored the inhibition mechanism using the enzyme kinetics. The results showed that As inhibition of soil ALP activity was substrate concentration-dependent. Increasing substrate concentration decreased inhibition rate, suggesting reduced toxicity. This dependency was due to the competitive inhibition mechanism of As to soil ALP. The kinetic parameters, maximum reaction velocity (V max ) and Michaelis constant (K m ) in unpolluted soils were 0.012-0.267mMh -1 and 1.34-3.79mM respectively. The competitive inhibition constant (K ic ) was 0.17-0.70mM, which was lower than K m , suggesting higher enzyme affinity for As than for substrate. The ecological doses, ED 10 and ED 50 (concentration of As that results in 10% and 50% inhibition on enzyme parameter) for inhibition of catalytic efficiency (V max /K m ) were lower than those for inhibition of enzyme activity at different substrate concentrations. This suggests that the integrated kinetic parameter, catalytic efficiency is substrate concentration independent and more sensitive to As than ALP activity. Thus, catalytic efficiency was proposed as a more reliable indicator than ALP activity for risk assessment of As pollution., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Diesel is a commonly used fuel and a key pollutant on water surface through leaks and accidental spills, thus creating risk directly to planktons as well as other aquatic organisms. We assessed the toxicty of diesel and its water accommodated fraction (WAF) towards two microalgal species, Pseudokirchneriella subcapitata and Chlorella sp. MM3. The toxicity criteria included were: chlorophyll a content as a growth parameter and induction of enzyme activities linked to oxidative stress. Increase in concentrations of diesel or its WAF significantly increased toxicity towards growth, measured in terms of chlorophyll a content in both the algae. Activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) in response to addition of diesel or diesel WAF to the microalgal cultures were dose-dependent. Diesel WAF was more toxic than diesel itself, suggesting that use of WAF may be more relevant for environmental risk assessment of diesel. The overall response of the antioxidant enzymes to toxicants' stress followed the order: POX≥SOD>CAT. The present study clearly demonstrated the use of SOD, POX and CAT as suitable biomarkers for assessing diesel pollution in aquatic ecosystem., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The leaf litters of tree species, Acacia pycnantha (Ap) and Eucalyptus camaldulensis (Ec), predominantly growing at an abandoned copper (Cu) mine and mine soils including controls, were assessed for determining the metal toxicity and bioavailability using earthworm species Eisenia fetida, in a microcosm. Significant reduction in body weight as well as mortality were observed when the worms were introduced into mine soil or its combination with mine Ap litter. Virtually, there were no juveniles when the worms were fed on substratum that contained mine soil or mine leaf litter. The extent of bioaccumulation was dependent on water-soluble fraction of a metal in soil. The accumulation of cadmium, lead and copper in worm tissue was significantly more in treatments that received mine soil with or without mine leaf litter. However, the tissue concentration of zinc did not differ much in earthworms irrespective of its exposure to control or contaminated samples. Mine leaf litter from Ec, a known Cu hyperaccumulator, was more hospitable to earthworm survival and juvenile than that of Ap litter. Validation of the data on bioaccumulation of metals indicated that the mine leaf litter significantly contributed to metal bioavailability. However, it was primarily the metal concentration in mine soil that was responsible for earthworm toxicity and bioavailability. Our data also indicate that detrivores like earthworm is greatly responsible for heavy metal transfer from mines into the ecosystem., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Zinc (Zn) is a widespread soil contaminant arising from a numerous anthropogenic sources. However, adequately predicting toxicity of Zn to ecological receptors remains difficult due to the complexity of soil characteristics. In this study, we examined solid-solution partitioning using pore-water data and toxicity of Zn to cucumber (Cucumis sativus L.) in spiked soils. Pore-water effective concentration (ECx, x=10%, 20% and 50% reduction) values were negatively related to pH, indicating lower Zn pore water concentration were needed to cause phytotoxicity at high pH soils. Total dissolved zinc (Znpw) and free zinc (Zn(2+)) in soil-pore water successfully described 78% and 80.3% of the variation in relative growth (%) in the full dataset. When the complete data set was used (10 soils), the estimated EC50pw was 450 and 79.2 µM for Znpw and Zn(2+), respectively. Total added Zn, soil pore water pH (pHpw) and dissolve organic carbon (DOC) were the best predictors of Znpw and Zn(2+) in pore-water. The EC10 (total loading) values ranged from 179 to 5214 mg/kg, depending on soil type. Only pH measurements in soil were related to ECx total Zn data. The strongest relationship to ECx overall was pHca, although pHw and pHpw were in general related to Zn ECx. Similarly, when a solution-only model was used to predict Zn in shoot, DOC was negatively related to Zn in shoot, indicating a reduction in uptake/ translocation of Zn from solution with increasing DOC., (Copyright © 2015 Elsevier Inc. All rights reserved.)

PFOS is a toxic, persistent environmental pollutant which is widespread worldwide. PFOS contamination has entered the food chain and is interfering with normal development in man and is neurotoxic, hepatotoxic and tumorigenic. The earthworm, Eisenia fetida is one of the organisms which can help to diagnose soil health and contamination at lower levels in the food chain. Studying the chronic effects of sub-lethal PFOS exposure in such an organism is therefore appropriate. As PFOS bioaccumulates and is not easily biodegraded, it is biomagnified up the food chain. Gene expression studies will give us information to develop biomarkers for early diagnosis of soil contamination, well before this contaminant passes up the food chain. We have carried out mRNA sequencing of control and chronically PFOS exposed E. fetida and reconstructed the transcripts in silico and identified the differentially expressed genes. Our findings suggest that PFOS up/down regulates neurodegenerative-related human homologues and can cause neuronal damage in E. fetida. This information will help to understand the links between neurodegenerative disorders and environmental pollutants such as PFOS. Furthermore, these up/down regulated genes can be used as biomarkers to detect a sub-lethal presence of PFOS in soil. Neuronal calcium sensor-2, nucleoside diphosphate kinase, polyadenylate-binding protein-1 and mitochondrial Pyruvate dehydrogenase protein-X component, could be potential biomarkers for sub lethal concentrations of PFOS., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Burkholderia vietnamiensis C09V (B.V. C09V) was used to remove both crystal violet (CV) and Cu(II) because dye effluents often contain dyes and metal ions. Inhibiting the strain׳s growth through the biosorption of Cu(II) on B.V. C09V and promoting its growth by using CV as a carbon source led to the degradation of CV (30mg/L). It fell to 36.9 percent and the amount of Cu(II) (50mg/L) removed rose to 34.9 percent in the presence of both CV and Cu(II). This outcome is comparable to the single presence of CV and Cu(II). EDS analysis showed that Cu(II) was adsorbed onto the strain (the atomic percentage of Cu(II) was 1.9 percent), while kinetic studies indicated that firstly, the decolorization of CV fitted well to the pseudo first-order degradation kinetic model and secondly, the biosorption of Cu(II) fitted well to the pseudo second-order kinetic model. The degradation rate constants of CV were stable in the 0.101-0.0068/h range and R(2) was both higher than 0.981 when Cu(II) concentrations were present. Furthermore, the biosorption capacity of Cu(II) ranged from 38.8 to 20.3mg/g at the CV concentration of 30mg/L (both R(2)>0.96). This suggests that the strain has the potential to degrade CV and facilitate the biosorption of Cu(II) in dye effluent., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Copper (Cu) is a widespread soil contaminant that is known to be highly toxic to soil biota. Limited information is available on the response of wild endemic species to Cu in the literature, which hinders ecological risk assessments and revegetation. In the present study, the phytotoxicity of Cu in nutrient solution was studied in five Australian endemic plant species (Acacia decurrens, Austrodanthonia richardsonii (Wallaby Grass), Bothriochloa macra (Redgrass), Eucalyptus camaldulensis var. camaldulensis (River Red-Gum) and Dichanthium sericeum (Bluegrass) and two vegetable plants species (Lactuca sativa L. 'Great lakes' and Raphanus sativa L.). Vegetable species were grown in a more concentrated nutrient solution. The response of B. macra was also compared between the two nutrient solutions (dilute and concentrated nutrient solution). In the first experiment, D. sericeum and E. camaldulensis were found to be highly sensitive to Cu exposure in nutrient culture. Critical exogenous Cu concentrations (50 percent reduction in roots) for E. camaldulensis, D. sericeum, A. richardsonii, B. macra (dilute), L. sativa, B. macra (concentrated), R. sativa and A. decurrens were, respectively, (μg/L) 16, 35, 83, 88, 97, 105, 128 and 186. Copper tolerance in B. macra was observed to be higher in the more concentrated nutrient solution despite the estimated Cu(2+) concentration being very similar in treatment solutions. Additional short-term rhizo-accumulation studies showed that neither Ca(2+) not K(+) was responsible for reduced uptake at the roots. However, the estimated maximum shoot Cu was reduced from 41 to 24mg/kg in the more concentrated solution., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The strain, Burkholderia vietnamiensis C09V was immobilized on PVA-alginate-kaolin gel beads as a biomaterial to improve the degradation of crystal violet from aqueous solution. The results show that 98.6% (30 mg L(-1)) crystal violet was removed from aqueous solution using immobilized cells on PVA-alginate-kaolin gel beads, while 94.0% crystal violet was removed by free cells after degradation at the pH 5 and 30°C for 30 h. Kinetics studies show that the pseudo-second-order kinetics well described the adsorption of crystal violet on the PVA-alginate-kaolin beads. Biodegradation of crystal violet on immobilized cells was fitted well by first-order reaction kinetics, indicating that CV was adsorbed onto kaolin and followed their degradation by immobilized cells onto the the PVA-alginate-kaolin beads. Characterization with SEM shows that cells attached well to the surface of PVA-alginate-kaolin beads, leading to improved crystal violet transfer from aqueous solution to immobilized cells. In addition, UV-vis show that the absorption peak at 588 nm was reduced by the degraded N-bond linkages, as well as the formation of degrading products were observed by Fourier transform infrared (FTIR). These results suggest that crystal violet was biodegraded to N,N-dimethylaminophenol and Michler's Ketone prior to these intermediates being further degraded., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Long-term lead (Pb) contaminated soils from two lead-zinc smelters and a shooting range, along with freshly spiked control soil, were studied by means of chemical, biological or a physiological method to examine the effect of ageing on Pb bioavailability. The freshly Pb spiked control soil was subjected to an earthworm toxicity test to observe the avoidance and mortality response of the earthworms. Meanwhile, an extractable fraction of Pb on the spiked soil as a result of ageing was examined and further compared with physiologically based in vitro bioaccessibility extraction tests. Their differences in lethal concentration, LC(50), to the earthworm population from spiked soils varied substantially as a function of soil pH. The strong effect of ageing on toxicity was also reflected in the extractability of Pb which was far greater in acidic soil, labelled AC, compared to the alkaline soil, labelled BC. This demonstrates that the bioavailable fraction causing toxicity to earthworms was achieved at a much lower total Pb content for acidic soils relative to alkaline soils. Moreover, the effect of ageing also exhibits that a marked decline in bioavailable Pb results in lowering toxicity. Significant amounts of weight loss in earthworms during an acute toxicity test in long-term contaminated soils at a relatively low Pb concentration suggested that other metal or combined metal toxicity may also play a significant role. This study demonstrates that the soil characteristics and ageing period greatly influence the bioavailable fraction of Pb which is related to the bioreceptor., (Copyright © 2011 Elsevier Inc. All rights reserved.)