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Dodecylbenzene sulfonate (DBS) is a component of linear alkylbenzene sulfonate (LAS), an anionic surfactant, mainly used in household detergents. Due to the large quantity of DBS in use, there is concern over adverse environmental effects. This work examined the toxicokinetics and toxicity of the 2-phenyl isomer of dodecylbenzene sulfonate in 4-d, 10-d, and partial life-cycle tests on the midge, Chironomus riparius, exposed to aqueous solutions. Toxicokinetics were determined in 10-d uptake and 5-d elimination tests. The toxicokinetics were based on parent compound concentration in water and yielded an uptake coefficient (k u ) of 17.5 (14.87-20.20) ml/g/h, an elimination rate constant (k c ) of 0.073 (0.062-0.085) per h, a bioconcentration factor (BCF) of 56 to 240, and a half-life (t 1/2 ) of 9.5 (8.0-11.0) h. Biotransformation measurements did not reveal evidence for DBS metabolism. Thus, body residues, determined in the toxicity study, represent parent compound. In toxicity tests, 4- and 10-d LR50s (the body residue required to cause 50% mortality) in live midges were 0.72 (0.65-0.79) and 0.18 (0.08-0.42) mmol/kg, respectively. Thirty-day LR50s were 0.18 (0.09-1.64) and 0.21 (0.15-0.39) mmol/kg in duplicate studies. Of the sublethal endpoints, only developmental time increase was significant, with the lowest-observed-effect residues of 0.085 (0.067-0.105) and 0.100 (0.087-0.114) mmol/kg for male and female midges, respectively. Deformities in surviving larvae were also observed as chronic responses for body residues exceeding the 30-d LR50. The body residues required for mortality suggest that DBS acts like a polar narcotic in the midge.

The location and activity of esterase enzymes in activated sludge from three municipal wastewater treatment plants were characterized using model substrates and denaturing and non-denaturing polyacrylamide gel electrophoresis (PAGE) of particulate, freeze-thaw (primarily periplasmic enzymes and those associated with outer cell surfaces) and extracellular fractions of activated sludge bacteria. Particulate and freeze-thaw fractions had a similar spectrum of substrate specificity and contained significant levels of protein and esterase activity against model substrates, C2-C18 monoesters of p-nitrophenol and C2-C8 diesters of fluorescein. Esterase activity was highest with substrates that had short alkyl chains (C4) and decreased as the chain lengths increased beyond C8. Extracellular fractions contained very low levels of protein (0.1 mg/l) and showed no esterase activity against any of the model substrates tested. Multiple bands were observed upon analysis of particulate and freeze-thaw fractions by non-denaturing PAGE in combination with activity staining using various alpha-naphthol ester substrates (C2-C8). Our results indicate that esterase enzymes in activated sludge are fairly diverse from a structural standpoint but exhibit a high level of functional redundancy, with different enzymes catalyzing the same reactions in different sludges. Extracellular esterase activity was totally absent for the substrates we tested and the esterase activity that we observed was closely linked to a particulate floc or cellular material.

Various methods used to assess the biodegradability of chemicals often employ activated sludge as an inoculum since chemicals that ultimately enter the environment are often discharged through wastewater. Differences in the structure and function of activated sludge microbial communities that may complicate interpretation of biodegradation tests could arise from differences in wastewater composition, wastewater treatment plant (WWTP) operation, or manipulations done after collection of the activated sludge. In this study, various methods were used to characterize the structure of microbial communities found in freshly collected activated sludge from WWTPs in Japan, Europe, and the United States, as well as sludge that had been continuously fed either sewage or a glucose-peptone mixture for several weeks after collection. Comparisons of biomass levels, whole-community substrate utilization (determined using Biolog GN and GP plates), and phospholipid fatty acid (PLFA) profiles indicated there were both geographical and temporal differences among freshly collected activated sludge samples. Moreover, marked shifts in the structure of activated sludge microbial communities occurred upon continuous cultivation in the laboratory for 5 weeks using a glucose-peptone feed. These shifts were evident from whole-community substrate utilization and PLFA profiles as well as differences in the profiles of 16S rDNA genes from numerically dominant populations obtained by denaturing gradient gel electrophoresis and terminal restriction fragment analyses. Further studies are needed to better define the variability within and between activated sludge from wastewater treatment plants and laboratory reactors and to assess the impact of such differences on the outcome of biodegradability tests.

Various mathematical relationships have been used to assess exposure concentrations of organic chemicals when emissions occur via wastewater treatment. These relationships range from a simple removal factor calculation to more sophisticated approaches using kinetic based mathematical models. While these existing approaches have been used by decision makers to screen new chemicals for exposure assessments, they all have limitations in the predictive capabilities. Thus, a simplified modeling approach grounded in sound scientific fundamentals that utilizes relatively easy to obtain input parameters is needed. In this paper a simplified modeling approach that utilizes microbial growth kinetics was developed for predicting effluent concentrations in secondary biological wastewater treatment systems. Receiving water predicted exposure concentrations (PEC) are assessed by using a dilution factor. One advantage of this approach is that it allows for wastewater treatment plant effluent concentrations, and therefore receiving water exposure levels, to be predicted with a minimum amount of experimental data. It also provides quantitative data that can be used to assess the relative biodegradability of different chemicals for use in regulatory and risk assessment activities.

An in-depth biodegradation test program was executed on the hexadentate ligand Ethylene Diamine Di Succinate (EDDS). The EDDS structure contains two chiral carbon atoms, and has three stereoisomers ([R,R], [R,S]/[S,R], [S,S]). Our research has focused on the isomer mixture (i.e. 25%[S,S]; 25%[R,R]; 50%[S,R]/[R,S], as produced from the reaction of ethylene diamine with maleic anhydride) and on the single [S,S]- and [R,R]-isomers. Biodegradation screening of the 14C-labelled EDDS isomer mixture in a Batch Activated Sludge (BAS) test with various inocula revealed incomplete mineralization, up to ca. 65% after 28 days. N-(2-aminoethyl) aspartic acid (AEAA), probably the d-isomer, was identified as the major portion of the 14C-material remaining in solution. Further testing revealed that the [S,S]-isomer is rapidly and completely mineralized in all test systems. By contrast, [R,R]-EDDS remained undegraded in a Sturm (OECD 301B) test, but was very slowly biotransformed into the recalcitrant metabolite AEAA in a BAS test. The [S,R]/[R,S] form undergoes biotransformation to AEAA in both high and low biomass systems. In a sewage treatment simulation test (OECD 303) the steady state DOC removal of mixture-EDDS in a CAS test was limited to 25-35%, even after extensive pre-acclimation, while the [S,S]-isomer achieved nearly complete removal (96%). This study illustrates the importance stereospecificity may have on the biodegradation and metabolite formation of a chemical. A biodegradation scheme for the different EDDS stereoisomers is proposed.

A two-step procedure is described to characterize the removal and biodegradation potential of nonvolatile 14C-labeled organic compounds in activated sludge. In the first step, trace concentrations of radiolabeled test materials are dosed in influent wastewater to continuous-flow activated sludge (CAS) systems which have been previously exposed or acclimated to unlabeled test material. Radiolabel is quantified in influent, effluent, and activated sludge mixed liquor to determine total 14C removal and partitioning of radiolabel in solid and liquid compartments. The 14C data are used to calculate the amount of removal due to sorption and biodegradation and to estimate the apparent sorption coefficients for 14C activity to activated sludge solids. The 14C-labeled CAS studies are followed by biodegradation studies in batch-activated sludge (BAS) systems using sludge derived from the CAS system. The kinetics of biodegradation (defined as mineralization to 14CO2) are measured in the BAS system to confirm the CAS biodegradation results and generate mineralization rate constants for kinetic modeling. The two-step procedure was applied to radiolabeled anionic (linear alkylbenzene sulfonate) and cationic (dodecyltrimethylammonium chloride, distearyldimethylammonium chloride) surfactants which differed greatly in their biodegradation and sorption profiles. Laboratory removal figures for these materials were comparable to values measured in full-scale wastewater treatment systems, although the amount of removal due to sorption and biodegradation varied significantly for the different surfactants. In general, the 14C method has several advantages over standard methods used in the United States and Europe which employ unlabeled materials. These advantages include the use of realistic concentrations and test conditions for acclimating and dosing activated sludge microorganisms and the ability to generate partitioning and kinetic constants that can be used more broadly in environmental fate and exposure models.

This paper introduces the environmental safety database for a new fabric softening cationic surfactant, the di-(tallow fatty acid) ester of di-2-hydroxyethyl dimethyl ammonium chloride, DEEDMAC > D i e thyl E ster D imethyl A mmonium C hloride). The physiochemical properties of DEEDMAC are similar to those for ditallow dimethyl ammonium chloride (DTDMAC), the major cationic surfactant used in fabric softener formulations world-wide for over thirty years. Importantly, however, DEEDMAC differs structurally from DTDMAC by the inclusion of two weak ester linkages between the ethyl and tallow chains. These ester linkages allow DEEDMAC to be rapidly and completely biodegraded in standard laboratory screening tests and a range of environmental compartments. including raw sewage, activated sludge, anaerobic digestor sludge, sludge amended soil, and river waters. Removal of DEEDMAC during sewage treatment is greater than 99%, as determined by computer model predictions and confirmed by laboratory simulation testing (OECD Continuous Activated Sludge confirmatory test). Using estimated tonnages, per capita waste water flows, incidences of sewage treatment for individual countries, measured removal rates, and validated computer models, maximum river water and soil concentrations of DEEDMAC have been estimated for representative usage scenarios. Based upon these maximum predicted environmental concentrations, acute and chronic toxicity testing offish, invertebrates and algae, predicted aquatic safety factors range from 272 to > 1000. Predicted steady state terrestrial safety factors are > 1000, based on EC50 values to earthworms and plants >50 mg/kg. The environmental safety database developed for DEEDMAC indicates that this cationic surfactant is rapidly and completely biodegraded, will be highly removed during sewage treatment. has an ecotoxicity profile similar to broadly used anionic and nonionic surfactants, and is environmentally safe at intended maximum usage volumes.

To ensure the environmental safety of new and existing substances, the environmental fate and potential effects resulting from their release into the environment must be assessed. This requires the development of reasonable, consistent, and effective methods to conduct environmental risk assessments and to prioritize testing for these substances. This assessment must integrate fate and effects at the point-of-entry; it should also extend to an assessment of the potential to persist, and the consequences of increases in exposure concentrations, and to bioaccumulate. The conventional environmental risk assessment approach is used to assess the fate and effects of a substance at its point-of-entry into the environment. In this paper, an approach is presented for conducting quantitative environmental risk assessments of new and existing substances that builds on this conventional, approach by including quantitative assessment of the potential for, and consequences of, persistence and bioaccumulation. The approach is described for aquatic, sediment, and terrestrial environments. For each environmental compartment, the approach includes (i) classification of the substance, based on environmental partitioning processes, to ensure that the appropriate data are collected and models used; (ii) a fate assessment to understand the ultimate fate of the substance after entry into the environment or "an environmental compartment" and to predict the exposure concentration of the substance at point-of-entry; (iii) a persistence assessment which determines the potential for increase in the exposure concentration as a result of repeated additions of the substance; (iv) effects assessment; (v) environmental risk assessment to examine the potential for adverse impact on ecosystems; and (vi) a bioaccumulation assessment to evaluate the potential for direct and indirect effects on the species of interest due to bioaccumulation. The assessment approach is illustrated using data for a hypothetical consumer product substance that is disposed down-the-drain.

This paper reviews the kinetics of biodegradation of linear alkylbenzene sulfonate (LAS) in engineered (wastewater treatment) and natural environment systems, focusing on work conducted in our environmental laboratories over the past 10–15 yr. Biodegradation studies were conducted in laboratory microcosms in which pure-chainlength [14C]-ring-labeled LAS homologs were used to allow complete mineralization to be assessed. In general, biodegradation rates for a series of LAS homologs (C10–C14) were comparable to each other and to values for naturally occurring materials such as sugars and fatty acids. Half-lives for LAS mineralization ranged from 1–2 d in aerobic and anaerobic sewage sludges, river water and sediments, to 1–3 wk in surface and subsurface soils and estuarine environments. The half-life for LAS degradation in different environmental compartments, relative to its residence time in these compartments, makes biodegradation a practically significant removal mechanism in a broad range of aquatic, benthic and terrestrial habitats.

The WW-TREAT model was developed to predict the fate of consumer product chemicals in primary and activated sludge wastewater treatment plants using independently determined values for the distribution coefficient between sludge solids and liquid, Henry's law constant and biodegradation rate constants. The major difference between this model and previous models is that it assumes the total chemical, not just the dissolved chemical, is available for biodegradation and that sorption to sludge solids increases the time that a chemical is available for biodegradation. The model was validated with monitoring data for four chemicals which possess sorption and biodegradation characteristics that span the range typical of the broader class of consumer product chemicals. Sensitivity analysis revealed that the most important parameters were the plant operating parameter, sludge/solids retention time and the chemical specific parameters, distribution coefficient and biodegradation rate constants. The sludge/solids retention time had its greatest effect when it was less than 9 days and the distribution coefficient had its greatest effect when it was between 100 and 3000 l/kg. The model predicted removal in primary and activated sludge wastewater treatment plants within 5%. Thus, the model can be used as a valuable tool for predicting the fate of consumer product chemicals.

The biodegradation activity of activated sludge was characterized by the API-ZYM and LRA-ZYM Esterase test systems. These systems provide rapid, semiquantitative information on the activity of hydrolytic enzymes associated with the biodegradation of lipids, proteins, carbohydrates, nucleic acids, and xenobiotic chemicals. Activated sludge was collected from several municipal wastewater treatment plants (WTPs) which varied with respect to their operating parameters and influent wastewater composition. Sludge samples were separated into various fractions (mixed liquor, sonicated mixed liquor, freeze-thaw, and extracellular fractions) and then assayed for enzyme activity relative to inactivated controls

The effect of linear alkylbenzene sulfonate (LAS) on the structure and function of microbial communities was studied in a flow-through model ecosystem containing several trophic levels. The LAS was supplied to 19-litre glass aquaria at 0.5 and 5.0 mg/litre in either well water (Phase I) or sewage effluent (Phase II). The structure of microbial populations was estimated from measurements of total viable biomass; function assays consisted of measuring rates of glucose or LAS degradation, or both. Assays of microbial function were also carried out in waters from two rivers. The results of Phase I studies indicated that LAS had no effect on microbial structure at either dose level. Microbial function was also unaffected at the low-dose level, although both glucose and LAS degradation were inhibited at the high-dose level. By contrast, 5 mg/litre LAS had no effect on microbial function in river water exposed to sewage effluent, as measured by the rate of LAS degradation. Similarly, there was no decrease in function of the microbial populations exposed to ∼5 mg/litre LAS in the Phase II model ecosystem. It was further noted that the overall kinetics of LAS degradation in Phase II model ecosystems were essentially identical to those in two river waters. From Phase I and Phase II studies the following were concluded: 1. Function measurements were preferable to structure measurements in characterizing mixed microbial communities. 2. The function of microbial communities in relatively simple model ecosystems closely approximates that of natural populations in surface waters.

The response of microbial communities to three classes of surfactants was studied in a stream and lake ecosystem. Dodecyltrimethylammonium chloride (TMAC, cationic) had no effect on bacterial biomass or carbon turnover inthe sediment, water column, or epilithon in a first-order stream that was continuously dosed with TMAC for 23 days. Biodegradation of TMAC was evident at all sites and showed a time-dependent increase only at the highest (0.25 mg/L) dose site. The effects of long-chain nonionic (linear primary alcohol ethoxylate: Neodol 45-7) and anionic (linear alkylbenzene sulfonate) surfactants were studied in situ in Acton Lake, Ohio. The chemicals were tested over a concentration range of 0.001 to 10 mg/L in both short-term (3 h) and long-term (21 day) exposures. Neither of the chemicals had averse effects on the microbial biomass as measured by acridine orange direct counts. In the acute test of these chemicals, decreased turnover of glucose was noted in the concentration range of 0.1 to 10 mg/L surfactant. However, in chronic tests (21 day) the communities recovered, and carbon turnover returned to preexposure levels. Chronic exposure also resulted in an adaptive response as indicated by increased degradation of the chemicals after exposure. Our studies indicate that exposure of lake and stream microbial communities to surfactants had no long-term detrimental effects on bacterial heterotrophy and resulted in increased biodegradation of these materials.

The kinetics of mineralization of uniformly 14 C-ring-labeled linear alkylbenzenesulfonate (LAS) were studied in river water and sediments for a series of pure chainlength homologues and phenyl isomers containing 10-14 carbon atoms in the alkyl chain

Dodecylbenzene sulfonate (DBS) is a component of linear alkylbenzene sulfonate (LAS), an anionic surfactant, mainly used in household detergents. Due to the large quantity of DBS in use, there is concern over adverse environmental effects. This work examined the toxicokinetics and toxicity of the 2-phenyl isomer of dodecylbenzene sulfonate in 4-d, 10-d, and partial life-cycle tests on the midge, Chironomus riparius, exposed to aqueous solutions. Toxicokinetics were determined in 10-d uptake and 5-d elimination tests. The toxicokinetics were based on parent compound concentration in water and yielded an uptake coefficient (ku) of 17.5 (14.87-20.20) ml/g/h, an elimination rate constant (ke) of 0.073 (0.062-0.085) per h, a bioconcentration factor (BCF) of 56 to 240, and a half-life (t 1/2) of 9.5 (8.0-11.0) h. Biotransformation measurements did not reveal evidence for DBS metabolism. Thus, body residues, determined in the toxicity study, represent parent compound. In toxicity tests, 4- and 10-d LR50s (the body residue required to cause 50% mortality) in live midges were 0.72 (0.65-0.79) and 0.18 (0.08-0.42) mmol/kg, respectively. Thirty-day LR50s were 0.18 (0.09-1.64) and 0.21 (0.15-0.39) mmol/kg in duplicate studies. Of the sublethal endpoints, only developmental time increase was significant, with the lowest-observed-effect residues of 0.085 (0.067-0.105) and 0.100 (0.087-0.114) mmol/kg for male and female midges, respectively. Deformities in surviving larvae were also observed as chronic responses for body residues exceeding the 30-d LR50. The body residues required for mortality suggest that DBS acts like a polar narcotic in the midge.

A batch method was developed and validated for determining the sorption coefficient (Kd) of biodegradable organic compounds to activated sludge solids using a nonspecific analytical technique, total organic carbon (TOC) analysis. In this method, activated sludge solids were first inactivated by lyophilization and dry heat (103 degrees C) and then washed to remove any dissolved organic carbon released during the inactivation procedure. The inactivated sludge solids were exposed to a range of concentrations of different test compounds in synthetic wastewater until equilibrium was achieved (2 h). The amount of test compound sorbed to the solids was then determined by measuring TOC levels in centrifuged supernatants. Results revealed that the sorption coefficients (Kd values) for four detergent chemicals in inactivated sludge solids using TOC analysis were in good agreement with values determined in fresh activated sludge using radiolabeled materials. These Kd values are suitable for use in estimating environmental exposure concentrations and for developing screening-level models to assess the removal of organic compounds by sorption and settling during activated sludge wastewater treatment.

The kinetics and efficiency of carbon dioxide recovery in modern versions of the Sturm Ready Biodegradation Test were examined to determine the ability of CO 2 evolution measurements to accurately estimate the rate and extent of ultimate biodegradation (mineralization). Kinetic data were analyzed by nonlinear regression techniques using an automated curve-fitting package available from commercial sources. The kinetics of CO 2 recovery in standard 3.8 L glass carboys containing 2 L of medium were rapid when headspace aeration (∼6 ml/min) and moderate agitation (140 rev/min) on a rotary platform shaker were used to ensure adequate aeration and mixing. The time (half-life) for 50% CO 2 recovery in external base traps was 4–5 hours, and stoichiometric recoveries of CO 2 equivalents added as bicarbonate were obtained within 24 hours. The kinetics of CO 2 evolution during biodegradation of several test compounds were significantly slower than the kinetics of CO 2 recovery, with half-lives between 65 and 191 hours. Our results indicate that mass transfer limitations do not impact CO 2 recoveries or biodegradation kinetic measurements in modern versions of the Sturm Test, even in test vessels with relatively low surface area to volume ratios (1:1). The use of headspace aeration and mixing generates reliable kinetic data, which can be analyzed by commercially-available nonlinear regression packages to provide rate information for the classification of chemicals with different biodegradation profiles.

The biodegradability of a substance depends on the structure and physical form of the substance, the time that has been available for acclimation, and the environmental conditions. Importantly, these later factors can be just as important as structure in determining the outcome of a biodegradation test. The development of appropriate QSARs for biodegradation and the ultimate value of the final QSAR depends on understanding these factors. This paper will describe what is known about the effect of test conditions on the results of biodegradation tests. The ability of these tests to reflect real environmental conditions will also be examined. Finally, we will discuss what we believe, in the light of this information, should be the goal of biodegradation QSARs and how these QSARs can be most appropriately used in fate assessments.

Source: https://erdc-library.erdc.dren.mil/jspui/ The geologic and geomorphic history of coastal areas can be assessed using a four-part process: o Thorough examination of technical literature and existing data from various archives. o Field data collection and observation. o Laboratory examination of samples collected in the field. o Office interpretation of all project data, both newly collected and historic. It is vital that existing sources of data be evaluated before field studies are undertaken to prevent duplicating efforts and to guide the· optimum sampling scheme. Field studies must be designed to answer basic questions about the study area: o What physical processes affect the region? o Does the underlying geology have a major influence? o How has man modified or damaged the local environment? o How much data can we afford to collect? o Do we have the knowledge, ability, managerial skill, or money to properly analyze the data we want to collect at the project site? o Is it more important to conduct a long-term sampling program or a shorter, more intensive program? Coastal scientists must be aware of how historic data were collected, and what assumptions and procedures were used by the original field technicians and analysts. The quality of historic data may vary from excellent to worse than useless. The use of instruments in the coastal zone is far from straightforward; incorrect use of instruments may lead to erroneous results because the wrong parameters may be monitored. Coastal engineers are urged to consult specialists in the field to help plan and conduct field studies. The analysis of contemporary coastal data is difficult and also requires the skills of specialists with experience in the particular types of instruments and methods that have been used.

Biodegradation is an important removal mechanism for consumer product chemicals released in large volumes to aquatic and terrestrial environments. It results in a decrease in the mass or load of chemicals present in the environment and is key in preventing accumulation and persistence of chemicals. Although biodegradation is an important process in minimizing potentially adverse impacts on environmental systems, it has not been traditionally considered quantitatively in environmental assessments. Efforts to use such data have principally focused on either wholly qualitative evaluations of a material's biodegradation properties (e.g., “fast” or “slow”), or rigorous quantitative models to predict exposure concentrations in particular settings. This paper outlines an alternative approach which provides a semi-quantitative analysis combining biodegradation rate data with an assessment of environmental exposure. The approach is a generic one that relates biodegradation half-lives to rates of transport and residence times in specific environmental compartments (e.g., agricultural soil, rivers). It establishes the kinetic criteria needed to make biodegradation a “practically significant” removal mechanism in a given environmental compartment. It is broadly applicable to chemicals which exhibit pseudo first order biodegradation kinetics at realistic environmental concentrations.

The adaptation of suspended microbial communities to a quaternary ammonium surfactant, dodecyltrimethylammonium chloride (C-12TMAC), was studied in a model stream dosed with the surfactant. Water collected at several sites downstream of the introduction of C-12TMAC was tested for the ability of the suspended microbial community to biodegrade the surfactant and several naturally occurring chemicals. At the concentrations tested, C-12TMAC had no significant impact on the total size of the microbial community or its ability to degrade natural materials (glucose or amino acids). However, the ability of the community to degrade C-12TMAC increased by 10- to 1,000-fold during exposure at all locations downstream from the dose site. After prolonged exposure, the C-12TMAC-degrading microbial community also developed a resistance to “shock loads” of the surfactant (i.e., adaptation was maintained even when input concentrations were increased to levels that previously decreased biodegradation activity). Adaptation was a stable process as long as some quantity of C-12TMAC entered the stream. However, when input of surfactant was halted, the microbial community lost its ability to rapidly degrade the material. Upon redosing the stream with a low concentration of the chemical, the microbial community rapidly regained its enhanced biodegradative activity toward C-12TMAC. These results illustrate the importance of adaptation in determining the fate of synthetic chemicals in aquatic environments.

The electrolytic respirometer was used to study the biodegradation of anionic, cationic and nonionic surfactants at ppm levels in Ohio River water. Below saturation or toxic concentrations, rates of oxygen consumption for all surfactants tested were directly proportional to surfactant concentration. Respiration data were fit by iterative techniques to a non-linear mathematical model to generate estimates of the rate constants for and extent of biodegradation. Estimates of biodegradability obtained from respiratory studies agreed well with estimates obtained in carbon dioxide evolution screening studies where surfactant was used as the sole carbon source by a sewage inoculum. The data indicate that the electrolytic respirometer can be used to measure biodegradation of complex organics in natural waters when specific analytical methods or radiolabelled materials are unavailable.

A method is described to estimate the biodegradation potential of soluble, insoluble, and unknown organic chemicals. The method consists of two stages: (i) generation of a microbial inoculum in a bench scale semicontinuous activated sludge system during which microorganisms are acclimated to test material and the removal of dissolved organic carbon is monitored and (ii) biodegradability testing (CO 2 evolution) in a defined minimal medium containing the test material as the sole carbon and energy source and a dilute bacterial inoculum obtained from the supernatant of homogenized activated sludge generated in the semicontinuous activated sludge system. Removal and biodegradation are measured using nonspecific methods, at initial concentrations of 5 to 10 mg of dissolved organic carbon per liter. Biodegradability data are accurately described by a nonlinear computer model which allows the rate and extent of biodegradation for different compounds to be compared and statistically examined. The evaluation of data generated in the combined removability-biodegradability system allows the biodegradation potential of a variety of xenobiotic organic chemicals to be estimated.

This paper reports the development of a method to determine the toxicity of chemicals to activated sludge. In the method, activated sludge was exposed to various concentrations of test chemicals and the inhibition of [14C]glucose uptake was measured after 15 min. Data for the decrease in glucose uptake as a function of the log of the test chemical concentration was analyzed by a nonlinear regression model to determine the concentration of chemical inhibiting uptake by 50% (IC50 value). In control experiments, glucose uptake in the absence of test chemicals was rapid, specific and totally dependent on the presence of metabolically-active activated sludge. However, uptake in the presence of inorganic and organic test chemicals showed significant, dose-dependent decreases as the concentration of test material increased. Inhibition of uptake was accurately described by the nonlinear regression model, and calculated IC50 values for two chemicals, mercuric chloride and 3,5-dichlorophenol, agreed well with values reported in the literature to adversely affect wastewater treatment plant operation. Based on the results of our studies, inhibition of glucose uptake proved to be a rapid, accurate and reproducible method of determining the toxicity of chemicals to activated sludge.

The biodegradation of nitrilotriacetic acid (NTA) was examined in three estuarine ecosystems, one of which had been exposed previously to the chemical. Biodegradation was measured as the conversion of radiolabeled NTA to 14CO2, 14C-labeled cells and the amount of label remaining in solution. The relatively unpolluted Newport River estuary system in North Carolina metabolized NTA slowly, with no apparent increase in rate over time. Jamaica Bay in New York showed an adaptation response, with approximately 50 d required for the onset of relatively rapid rates of biodegradation. The Fraser River estuary in Canada, exposed to NTA for more than 10 years, showed rapid degradation with no lag period at a concentration of 10 μg/L. At 100 and 2,000 μg/L, short lag periods (2 to 4 d) were observed before rapid degradation rates were achieved. Measurements of NTA-degraders indicated that the Fraser River estuary contained 650/ml versus fewer than 10 in the Newport River and Jamaica Bay communities. The results demonstrate that NTA can be degraded by estuarine microorganisms. Estuarine bacteria will adapt to the presence of NTA in the environment and, after adaptation, can respond to increased levels of the compound after relatively short lag periods.

The kinetics of ultimate biodegradation (mineralization to CO2) of linear alkylbenzene sulfonate (LAS) were studied in sludge-amended agricultural soils for a series of pure chain length LAS homologs containing 10 to 14 carbon atoms in the alkyl chain. Degradation rates were measured by following the production of 14CO2 from uniformly 14C-ring-labeled material. In general, degradation of LAS was rapid in soil over a broad concentration range (0.1 to 10 times the expected environmental concentration) and demonstrated little variation among different homologs. Half-lives for mineralization of the benzene ring ranged from 18 to 26 days and were not significantly different for any homolog over the range of alkyl chain lengths tested. Half-lives measured for LAS degradation in these studies were comparable to values reported in the literature and also to values obtained for naturally occurring materials (stearic acid, cellulose) typically present in soil environments. On the basis of the results of the present studies and those of other investigators, it is concluded that soil environments exposed to LAS in sewage sludges contain microbial communities which can actively metabolize this material. Rates of biodegradation of the benzene ring, the final step in the LAS biodegradation pathway prior to complete mineralization, are also sufficient to prevent LAS from accumulating in soil environments.

The number and metabolic diversity of bacteria were studied in groundwaters collected in the United States and Canada. Bacterial numbers were determined by acridine orange direct counts, viable plate counts and 14C most-probable-number counts. Metabolic diversity was determined by heterotrophic activity and biodegradation potential assays using several classes of natural and xenobiotic substrates. Rates of metabolism in diversity studies (uptake and/or mineralization to carbon dioxide) were measured by radiotracer techniques and rate data were analyzed by nonlinear regression models to generate appropriate kinetic constants. Overall, the density and activity of groundwater bacteria were comparable to values reported for oligotrophic marine and freshwater systems. Bacterial numbers ranged from approximately 102 to 106 cells/ml, depending on the enumeration technique used and the particular sample tested. Turnover times for natural compounds in heterotrophic activity assays (i.e., glucose, amino acids) ranged from less than 100 to more than 2,000 h. Degradation half-lives for xenobiotic and natural substrates in biodegradation potential studies exhibited a comparable range of values. In general, our results indicate that groundwater bacteria have the potential to metabolize several classes of natural and xenobiotic substrates, although at reduced rates compared with those of surface water systems.

The effect of temperature and dissolved oxygen on the rate of biodegradation of nitrilotriacetate (NTA) was examined in water samples collected from the Rur River. Biodegradation of NTA was first order with respect to NTA concentration over a concentration range of 50–1000 μg l −1 . First order rate constants showed a typical temperature dependency (temperature coefficient, Q 10 = 2) and biodegradation of NTA was observed over a temperature range of 2–24°C. The effect of temperature on the rate of NTA biodegradation was described by the Arrhenius equation, with calculated activation energies in the range reported for ordinary enzyme reactions. Biodegradation of NTA was also observed at low dissolved oxygen concentrations (0.3 mg l −1 ), although at reduced rates compared to high oxygen concentrations (13 mg l −1 ). Biodegradation of NTA was oxygen-dependent, suggesting an obligate oxygen requirement for the initial steps in NTA metabolism by natural microbial communities in surface waters. In general, our results indicate that NTA biodegradation will occur in natural waters under conditions of low temperature and low dissolved oxygen and also at low NTA concentrations.

Acclimation to and biodegradation of nitrilotriacetic acid (NTA), an organic builder used in synthetic laundry detergents as the sodium salt, was studied at trace concentrations (ppb) in several river waters. The river waters tested ranged from those where extensive NTA exposure via detergents had not occurred, to those where NTA exposure had been continuous for several years. In rivers not previously exposed to NTA, acclimation and degradation were observed at the lowest initial concentration tested, 5 μg 1 −1 . Degradation of NTA after acclimation followed apparent first order kinetics, and half lives for NTA removal ranged from 7 to 138 h at initial NTA concentrations of 50 and 5 μg 1 −1 , respectively. Degradation of NTA in water samples where prior NTA exposure had already occurred required no acclimation and was less variable than in unexposed rivers. First order rate constants varied only slightly over a 1000-fold initial concentration range (1–1000 μg 1 −1 ) and NTA half lives ranged from 7 to 17 h. In general, our results indicate that microflora present in natural waters can acclimate to and degrade NTA, even if exposed to only trace levels in laboratory experiments. However, rates of NTA biodegradation are more rapid and less variable in river waters where natural NTA exposure has already occurred.

Cobalt, like Mg, may cause the precipitation of aragonite rather than calcite in aqueous solutions due to the adsorption and crystal poisoning of calcite by a hydrated ion. Solutions containing NaCl and CaCl 2 , having the ionic strength and Ca content of seawater (35‰ salinity), were spiked with known amounts of CoCl 2 . Calcium carbonate was precipitated by the addition of 0.7 ml of 1 M Na 2 CO 3 . All experimental runs were made at 25°C, and all products were examined by X-ray diffraction. At low concentrations of Co ( −4 M ) calcite and vaterite formed. At concentrations from 5·10 −4 M to 2·10 −3 M , the products consisted of combinations of calcite and vaterite; aragonite and calcite; aragonite and vaterite; calcite, vaterite and aragonite. In solutions of 3·10 −3 M CoCl 2 , most precipitates were aragonite with only one sample containing a small amount of calcite. All precipitates from 5·10 −3 M CoCl 2 solutions either contained aragonite or were amorphous. Solutions with concentrations of 1 · 10 −2 M CoCl 2 produced only amorphous precipitates. All precipitates contained an amorphous violet phase, assumed to be basic cobaltous carbonate (2CoCO 3 ·Co(OH) 2 ·H 2 O).

The biodegradability of linear alkylbenzene sulfonate (LAS) was studied in water samples collected from a receiving stream at locations above and below the discharge of a municipal wastewater treatment plant. Rates of primary biodegradation were determined for a commercial LAS mixture by a modified methylene blue-active substance method. Rates of LAS ultimate degradation were determined by radiochemical methods, using a C 12 LAS homolog uniformly labeled with 14 C in the benzene ring. The C 12 LAS was tested at low concentrations (50 and 500 μg/liter) comparable to those existing in the receiving stream. Loss of methylene blue-active substance response over time occurred rapidly in water samples containing sediment collected from below the treatment plant, with an estimated half-life for LAS of 0.23 days. Evolution of 14 CO 2 during mineralization of the benzene ring occurred rapidly in the same samples, with a half-life for the benzene ring of 0.73 day. Mineralization of the benezene ring was also observed in river water containing no sediments and in river water and sediment samples collected from above the treatment plant. However, the rate of degradation was reduced in these cases, with half-lives for ring carbon ranging from 1.4 to 14 days. Although LAS degradation was enhanced in the presence of sediments, adsorption of LAS to the clay-silt fraction of river sediments was low, and most of the radioactivity was bound to biomass.

The effects of long-chain (C 12 to C 18 ) quaternary ammonium compounds (QACs) on the density, heterotrophic activity, and biodegradation capabilities of heterotrophic bacteria were examined in situ in a lake ecosystem. Monoalkyl and dialkyl substituted QACs were tested over a range of concentrations (0.001 to 10 mg/liter) in both acute (3 h) and chronic (21 day) exposures. In general, none of the QACs tested had significant adverse effects on bacterial densities in either acute or chronic studies. However, significant decreases in bacterial heterotrophic activity were noted in acute studies at QAC concentrations from 0.1 to 10 mg/liter. Chronic exposure of lake microbial communities to a specific monoalkyl QAC resulted in an adaptive response and recovery of heterotrophic activity. No-observable-effect level in the adapted populations was >10 mg/liter. Chronic exposure also resulted in significant increases in the number and activity of bacteria capable of biodegrading the material. The increase in biodegradation capability was observed at low (microgram per liter) concentrations which are approximately the same as realistic environmental levels. In general, our studies indicated that exposure of lake microbial communities to QACs results in the development of adapted communities which are less sensitive to potential toxic effects and more active in the biodegradation of these materials.

The effects of salinity and dissolved organic carbon (DOC) on the kinetics of biodegradation of nitrilotriacetic acid (NTA) were studied in a Canadian estuary with a prior history of NTA exposure. Kinetic parameters for degradation of /sup 14/C-labeled NTA, maximum velocity (Vmax) and first-order rate constant (k1), were estimated by nonlinear regression models from velocity and time-course plots, respectively. The distribution of bacteria with NTA-degrading capability was also determined at various salinities and DOC levels by the /sup 14/C-most-probable-number (/sup 14/C-MPN) technique. In general, NTA degradation was rapid in estuarine water over the range of salinities and DOC levels tested. Mean Vmax and k1 values (+/- standard deviation) across several sampling periods averaged 4753 +/- 2849 ng liter-1 hr-1 and 0.32 +/- 0.19 day-1, respectively. The estimated half-life for NTA degradation in estuarine water, based on the mean k1 value, was approximately 2 days. Degradation rates for NTA were relatively insensitive to changes in salinity or DOC values, and neither of these two parameters had significant effects on NTA degradation at the microbial community or individual cell levels. Based on /sup 14/C-MPN results, the distribution of estuarine bacteria capable of degrading NTA was broad and not related to salinity ormore » DOC levels. The NTA degraders appeared to be indigenous members of the estuarine microbial community and not wastewater-associated microorganisms.« less

The growth and morphology of cells of Asticcacaulis biprosthecum were studied in defined media to determine the effects of various compounds on the growth rate and on the expression of morphological events of the life cycle. The length of prosthecae could not be controlled by varying the concentration of inorganic phosphate as has been shown for other caulobacters. In defined media, growth was inhibited during conditions favoring rapid metabolism, apparently due to an absolute requirement for cells to complete all stages of the life cycle before cell division could occur. The morphology of cells grown under these conditions was aberrant, i. e., cells appeared elongated and branched and few prosthecae or swarmer cells were produced. Growth of a related bacterium, Asticcacaulis strain S-3, was not inhibited by conditions favoring rapid metabolism. During rapid growth, cell division in this organism occurs in the swarmer stage and prosthecae are not produced. Cell division in S-3 is not obligately coupled to completion of all stages in the complex life cycle, and morphogenesis can be controlled by cultural conditions.

Microbial degradation (biodegradation) of organic chemicals is generally recognized as an important removal mechanism in natural systems. For chemicals which reach the aquatic environment in significant quantities, estimates of biodegradability are key in assessing the overall hazard associated with the use of a particular chemical (Larson 1980). Estimates of biodegradability are often generated in the laboratory via biodegradability screening studies (Larson 1979). In screening studies, compounds are tested as sole carbon and energy sources at relatively high (mg/L) concentrations with a dilute synthetic salts solution as the test medium. Degradation is measured nonspecifically by following the amount of carbon dioxide produced or oxygen consumed during microbial metabolism, and soil or sewage are typically used as the source of degradative microorganisms. These experimental conditions do not accurately simulate natural aquatic environments, where chemical concentrations are low (μg/L) and a variety of nutrient conditions and microbial species exist. As a result, legitimate questions have been raised about the reliability of biodegradability screening tests, and the ability of such tests to predict fate of compounds in the “real world” (Alexander 1981).