Derivation of species sensitivity distributions and ecotoxicity threshold values for 66 pesticide active ingredients and the hazard and risk they pose to freshwater waterways that discharge to the Great Barrier Reef, Australia.

Pesticide active ingredients (PAIs) are one of the main contributors affecting water quality in the Great Barrier Reef Catchment Area (GBRCA). While an extensive list of pesticides is monitored in the GBRCA, only a limited number have water quality guideline values (WQGs), meaning it is not possible to know whether these PAIs are present at concentrations that may pose a hazard to the aquatic environment. In the current study, we derived 66 ecotoxicity threshold values (ETVs) for PAIs, the equivalent of WQGs, with a focus on PAIs applied to sugar cane. The hazard posed by PAIs monitored as part of the Great Barrier Reef Catchment Loads Monitoring Program (GBRCLMP) was assessed by comparing the derived ETVs with monitoring data from 2016/2017 to 2021/2022. The derived ETVs included herbicides, insecticides and fungicides, with the values that should protect 99 or 95 % of aquatic species (PC99 or PC95) spanning nine orders of magnitude. The concentrations of 10 PAIs exceeded their respective ETVs, giving a hazard quotient (HQ) >1. Of particular concern were insecticides chlorpyrifos, diazinon and methomyl, which have maximum HQ values >10. However, joint probability plots indicated that the PAIs generally pose a low risk to the aquatic environment, with most samples below the limit of reporting. As PAIs are predominantly found in mixtures in the GBRCA, the hazard posed by PAI mixtures was assessed by summing all individual HQ values in a sample for all PAIs with an ETV or WQG. On average, the insecticide active ingredient imidacloprid and herbicide active ingredients metolachlor, metsulfuron methyl, diuron and imazepic were the drivers of combined mixture hazard. Methomyl was an important contributor at some sites, suggesting that this pesticide should be considered for inclusion in any future PAI mixture hazard and/or risk assessment of the GBRCA.

Assessing the chronic toxicity of atrazine, permethrin, and chlorothalonil to the cladoceran Ceriodaphnia cf. dubia in laboratory and natural river water.

The majority of ecotoxicological data are generated from standard laboratory-based experiments with organisms exposed in nonflowing systems using highly purified water, which contains very low amounts of dissolved organic matter and suspended particulates. However, such experimental conditions are not ecologically relevant. Thus, there is a need to develop more realistic approaches to determining toxicity, including both lethal and sublethal effects. This research provides information on the effect of natural water constituents, such as suspended particulates and dissolved organic matter, in river water (RW) on the chronic toxicity (7-day reproductive impairment) of the pesticides atrazine, chlorothalonil, and permethrin to the freshwater cladoceran Ceriodaphnia cf. dubia. Standard bioassays were conducted under standard laboratory and more environmentally realistic conditions (using RW). The 7-day IC25 (reproduction impairment) values of atrazine, chlorothalonil, and permethrin to C. cf. dubia ranged from 862.4 to >1000, 51.3 to 66.4, and 0.19 to 0.23 µg/L, respectively. Using the Globally Harmonized System of Classification and Labelling of Chemicals, atrazine is classified as moderately to highly toxic, whereas permethrin and chlorothalonil were both highly toxic. The presence of dissolved organic matter and suspended particles in natural RW did not significantly (p > 0.05) change the toxicity of any of the pesticides to C. cf. dubia compared with that tested in laboratory water (LW). For the tested pesticides, toxicity testing in LW provided an adequate estimate of the hazard posed.

Estimating the aquatic risk from exposure to up to twenty-two pesticide active ingredients in waterways discharging to the Great Barrier Reef.

Pesticides decrease the quality of water reaching the Great Barrier Reef (GBR), Australia. Up to 86 pesticide active ingredients (PAIs) were monitored between July 2015 to end of June 2018 at 28 sites in waterways that discharge to the GBR. Twenty-two frequently detected PAIs were selected to calculate their combined risk when they co-occur in water samples. Species sensitivity distributions (SSDs) for the 22 PAIs to fresh and marine species were developed. The SSDs, the multi-substance potentially affected fraction (msPAF) method, Independent Action model of joint toxicity and a Multiple Imputation method were combined to convert measured PAI concentration data to estimates of the Total Pesticide Risk for the 22 PAIs (TPR22) expressed as the average percentage of species affected during the wet season (i.e., 182 days). The TPR22 and percent contribution of active ingredients of Photosystem II inhibiting herbicides, Other Herbicides, and Insecticides to the TPR22 were estimated. The TPR22 ranged from <1 % to 42 % of aquatic species being affected. Approximately 85 % of the TPR22 estimates were >1 % - meaning they did not meet the Reef 2050 Water Quality Improvement Plan's pesticide target for waters entering the GBR. There were marked spatial differences in TPR22 estimates - regions dominated by grazing had lower estimates while those with sugar cane tended to have higher estimates. On average, active ingredients of PSII herbicides contributed 39 % of the TPR22, the active ingredients of Other Herbicides contributed ~36 % and of Insecticides contributed ~24 %. Nine PAIs (diuron, imidacloprid, metolachlor, atrazine, MCPA, imazapic, metsulfuron, triclopyr and ametryn) were responsible for >97 % of TPR22 across all the monitored waterways.

Toxicity of Herbicide Mixtures to Tropical Freshwater Microalgae Using a Multispecies Test.

Agriculture within the Great Barrier Reef catchment area has contributed to pesticide contamination of adjacent freshwater ecosystems that flow into the Great Barrier Reef World Heritage Area. A novel multispecies toxicity test was used to assess the toxicity of diuron and hexazinone, 2 herbicides commonly detected within the Great Barrier Reef catchment area, to a community of 3 tropical freshwater microalgae: Monoraphidium arcuatum, Nannochloropsis-like sp., and Pediastrum duplex. Diuron was the most toxic herbicide, with 10% inhibition concentration (IC10) values of 4.3, 7.1, and 29 µg/L for P. duplex, M. arcuatum, and Nannochloropsis-like sp., respectively, followed by hexazinone, with IC10 values of 15, 18, and 450 µg/L, respectively Toxicity testing on 2 commercial formulations (Barrage, 13.2% hexazinone and 48.6% diuron; Diurex, 90% diuron) showed that additives in the commercial formulations did not significantly increase the toxicity of diuron. Direct toxicity assessments were carried out on water samples from the herbicide-contaminated Sandy Creek, which discharges to the Great Barrier Reef lagoon, and a clean reference site, Tully Gorge in the Tully River. Toxicity was observed in several Sandy Creek samples. Artificial herbicide mixtures were assessed in synthetic soft water and natural freshwaters, with toxic responses being observed at environmentally relevant concentrations. The present study successfully applied a novel multispecies tropical microalgal toxicity test, indicating that it is an effective tool for the assessment of herbicide toxicity in both natural and synthetic freshwaters. Environ Toxicol Chem 2021;40:473-486. © 2020 SETAC.

Analysis of pesticide mixtures discharged to the lagoon of the Great Barrier Reef, Australia.

Organisms and ecosystems are generally exposed to mixtures of chemicals rather than to individual chemicals, but there have been relatively few detailed analyses of the mixtures of pesticides that occur in surface waters. This study examined over 2600 water samples, analysed for between 21 and 47 pesticides, from 15 waterways that discharge to the lagoon of the Great Barrier Reef in Queensland, Australia between July 1, 2011 and June 30, 2015. Essentially all the samples (99.8%) contained detectable concentrations (>limit of detection) of pesticides and pesticide mixtures. Approximately, 10% of the samples contained no quantifiable (>limit of reporting) pesticides, 10% contained one quantifiable pesticide and 80% contained quantifiable mixtures of 2-20 pesticides. Approximately 82% of samples that contained quantifiable mixtures had more than two modes of action (MoAs), but only approximately 6% had five or more MoAs. The mode, average and median number of quantifiable pesticides in all the samples were 2, 5.1 and 4, respectively. The most commonly detected compounds both individually and in mixtures were the pesticides atrazine, diuron, imidacloprid, hexazinone, 2,4-D, and the degradation product desethylatrazine. The number of pesticides and modes of action of pesticides in mixtures differed spatially and were affected by land use. Waterways draining catchments where sugar cane was a major land use had mixtures with the most pesticides.

Development and application of a multispecies toxicity test with tropical freshwater microalgae.

Microalgae are commonly used in ecotoxicity testing due to their ease of culturing and rapid cell division rates. These tests generally utilise a single species of algae; however, microalgae occur in the environment as complex communities of multiple species. To date, routine multispecies toxicity tests using tropical microalgae have not been available. This study investigated four tropical freshwater microalgal species for use in a chronic multispecies toxicity test based on the population growth (cell division) rate: Pediastrum duplex, Monoraphidium arcuatum, Nannochloropsis-like sp. and Chlorella sp. 12. Flow cytometric analysis identified the different fluorescence and light scattering properties of each algal species and quantified each species within multispecies mixtures. Following optimisation of test media nutrients and pH, a toxicity testing protocol was developed with P. duplex, M. arcuatum and Nannochloropsis-like sp. There were no significant differences in growth rates of each alga when tested over 72 h as single species or in multispecies mixtures. Atrazine and imazapic, two herbicides with different modes of action, were used to assess the sensitivity of the multispecies toxicity test. Atrazine was toxic to all species with 72-h IC10 values of 7.2, 63 and 280 µg/L for P. duplex, M. arcuatum and Nannochloropsis-like sp. respectively, while imazapic was not toxic to any species at concentrations up to 1100 µg/L. The toxicity of atrazine and imazapic to each microalgal species in the multispecies toxicity test was the same as that determined from single-species toxicity tests indicating that the presence of these microalgae in a mixture did not affect the toxicity of these two herbicides. This study is the first to develop a multispecies tropical microalgal toxicity test for application in freshwaters. This time- and cost-effective tool can be utilised to generate data to assist environmental decision making and to undertake risk assessments of contaminants in tropical freshwater environments.

How we can make ecotoxicology more valuable to environmental protection.

There is increasing awareness that the value of peer-reviewed scientific literature is not consistent, resulting in a growing desire to improve the practice and reporting of studies. This is especially important in the field of ecotoxicology, where regulatory decisions can be partly based on data from the peer-reviewed literature, with wide-reaching implications for environmental protection. Our objective is to improve the reporting of ecotoxicology studies so that they can be appropriately utilized in a fair and transparent fashion, based on their reliability and relevance. We propose a series of nine reporting requirements, followed by a set of recommendations for adoption by the ecotoxicology community. These reporting requirements will provide clarity on the the test chemical, experimental design and conditions, chemical identification, test organisms, exposure confirmation, measurable endpoints, how data are presented, data availability and statistical analysis. Providing these specific details will allow for a fuller assessment of the reliability and relevance of the studies, including limitations. Recommendations for the implementation of these reporting requirements are provided herein for practitioners, journals, reviewers, regulators, stakeholders, funders, and professional societies. If applied, our recommendations will improve the quality of ecotoxicology studies and their value to environmental protection.

Toxicity and bioavailability of atrazine and molinate to the freshwater fish (Melanotenia fluviatilis) under laboratory and simulated field conditions.

Acute (96 h) semi-static toxicity tests were conducted by exposing the freshwater fish, Melanotenia fluviatilis, to atrazine and molinate in laboratory and river water both with and without sediment. The 96-h EC50 (imbalance) values of atrazine to M. fluviatilis ranged from 5.6 to 10.4 mg L(-1) while the corresponding values for molinate ranged from 7.9 to 14.8 mg L(-1), respectively. Atrazine was classed as having moderate toxicity while molinate had low to moderate toxicity to M. fluviatilis. Neither the presence of river water nor sediment significantly (P<0.05) reduced the bioavailability of either herbicide to M. fluviatilis. A series of other studies by the authors have found that sediment significantly (P<0.05) reduced the bioavailability of these two chemicals to a variety of organisms. Reasons for sediment having no effect for this species were examined. This lack of effect by sediment is most likely due to the relative rates of absorption into the fish and adsorption onto the sediment. However, contributions to this outcome by resuspended sediment, contaminated food and a combined effect of the herbicides and sediment could not be excluded.

Effect of river water, sediment and time on the toxicity and bioavailability of molinate to the marine bacterium Vibrio fischeri (Microtox).

The toxicity and bioavailability of molinate to Vibrio fischeri (Microtox((R))) were determined in both laboratory and river water in the absence and presence of sediment after 0, 24, 48, 72 and 96-h exposure. The bioavailability of molinate, expressed as 5min EC50s (bioluminescence) and their fiducial limits calculated using initial measured concentrations, to V. fischeri in laboratory water in the absence and presence of sediment ranged from 1.8 (1.7-2.1) to 3.6 (3.5-3.7) mgL(-1) and 1.3 (1.2-1.4) to 4.2 (3.5-4.5) mgL(-1), respectively. The corresponding values in river water and river water plus sediment were 1.7 (1.6-1.8) to 3.8 (3.6-4.1) and 1.3 (1.3-1.4) to 4.6 (4.2-4.9) mgL(-1), respectively. River water did not significantly (P>0.05) reduce the bioavailability of molinate to V. fischeri compared to that of laboratory water. However, the presence of sediment significantly (P<0.05) reduced the bioavailability of molinate to V. fischeri in both waters. The exposure time also significantly (P<0.05) reduced the bioavailability of molinate to V. fischeri in both waters in the presence and absence of sediment. The type of water did not significantly (P>0.05) affect the loss of molinate during the 96-h exposure period. However, the presence of sediment significantly (P<0.01) increased the loss of molinate from the test solutions, probably by binding to the sediment particles. Exposure period and concentration levels significantly (P<0.05) affected the loss of the herbicides over the 96h.

The toxicity and bioavailability of atrazine and molinate to Chironomus tepperi larvae in laboratory and river water in the presence and absence of sediment.

Acute (10 day) semi-static toxicity tests in which the midge, Chironomus tepperi, were exposed to atrazine and molinate were conducted in laboratory water and in river water, in the absence and presence of sediment. The bioavailability measured as median lethal concentrations (LC50) and 95% fiducial limits (FLs) of atrazine to C. tepperi in laboratory water in the absence and presence of sediment were 16.6 (14.3-19.4) and 21.0 (18.2-24.1) mg l(-1), respectively while the corresponding values in river water were 16.7 (14.7-19.0) and 22.7 (20.3-25.4) mg l(-1), respectively. For molinate, the LC50 and FL values in laboratory water in the absence and presence of sediment were 8.8 (6.8-11.4) and 14.3 (12.4-16.4) mg l(-1), respectively and the corresponding values in river water were 9.3 (7.6-11.3) and 14.5 (12.4-16.9) mg l(-1), respectively. Atrazine has low toxicity (LC50 > 10 mg l(-1)) while molinate has moderate toxicity (1 mg l(-1) < LC50 < 10 mg l(-1)) to C. tepperi. River water did not significantly (P > 0.05) reduce the bioavailability of either chemical to C. tepperi. However, the presence of sediment did significantly (P < 0.05) reduce the bioavailability of both atrazine and molinate to C. tepperi.

Comparison of the critical concentration and critical volume hypotheses to model non-specific toxicity of individual compounds.

The critical concentration and critical volume hypotheses for non-specific toxicity require the molar concentration (CC) and volume fraction (VF) of toxicant in target tissue to be constant. Thus these factors should be independent of the octanol-water partition coefficient (Kow) for individual compounds. CC and VF values were calculated based on acute sub-lethal, acute and chronic lethal toxicity data, Kow and pure component molar volume (MV) data. When these values were plotted against log Kow, the slopes of the regression equations were significantly different to zero but were not significantly different from each other. The observed slight increase in CC and VF with increasing log Kow was attributed predominantly, to the use of Kow values which overestimate the target tissue-water partition coefficient (Kow). An additional error associated with the volume fraction calculations was the use of the molar volume instead of partial molar volume. VF and CC values were calculated correcting for both these factors and regressed against log Kow. The resulting equation for VF had a gradient not significantly different from zero, while that for CC was, thus indicating the superiority of the critical volume hypothesis in modelling non-specific toxicity of individual compounds.

Quantitative structure-toxicity relationships for halogenated substituted-benzenes to Vibrio fischeri, using atom-based semi-empirical molecular-orbital descriptors.

Quantitative structure-toxicity relationships (QSTR's) are derived for an extensive series of halogenated benzenes, anilines, phenols, nitrobenzenes, toluenes and other substituted benzenes against Vibrio fischeri using a wide range of whole molecule and atom-based descriptors derived from semi-empirical molecular-orbital calculations. In terms of direct statistical correlation with toxicity it was found that the molar refractivity was the most important parameter, closely followed by the solvent accessible surface area of the compound. The accuracy of these descriptors in fitting the numerous fluoro- and chloro-mono-aromatic compounds was compared with bromine and iodine analogues, where the 'best' descriptors for the former were found in general to be less accurate for the latter in the case of multi-halogen substitution. The equations obtained were also used to classify the compounds into narcosis-based mechanisms of toxicity and those with respiratory uncoupling potential. A combination of the molar refractivity and the nucleophilic susceptibility of one of the meta ring carbons predicted the toxicity of the halo-benzenes and toluenes, along with anisoles, benzonitriles, nitrobenzenes and most of the anilines. The relevance of these descriptors to developing coherent and more generally applicable models for QSTR's of mono-aromatic compounds to other species in environmental toxicology is discussed.

The presence of chemicals exuded by fish affects the life-history response of Ceriodaphnia cf. dubia to chemicals with different mechanisms of action.

The toxicity of chemicals with different mechanisms of action (3,4-dichloroaniline, fenoxycarb, and chlorpyrifos) to the cladoceran Ceriodaphnia cf. dubia was examined in the presence and absence of chemicals exuded by fish, termed fish kairomones. A range of life-history traits were examined, including mean brood sizes, survival, net reproductive rate (Ro) and population growth rate (r). Cladocerans exposed to 3,4-dichloroaniline showed similar sensitivities in the presence and absence of fish kairomones with respect to all of the life-history traits examined. The presence of fish kairomones reduced the sensitivity of cladocerans to fenoxycarb with respect to mean brood sizes and r but increased their sensitivity in terms of Ro. The presence of fish kairomones increased the sensitivity of cladocerans to chlorpyrifos with respect to survival, r, Ro, and mean brood sizes. The general trends observed were similar to those shown when C. cf. dubia was exposed to these chemicals under low food conditions, and it is suggested that the effects of fish kairomones on toxicity may be attributed to the reduction in feeding rates observed when C. cf. dubia is exposed to fish kairomones.

Quantitative structure-activity relationships and volume fraction analysis for nonpolar narcotic chemicals to the australian cladoceran ceriodaphnia cf. dubia

The toxicity of eleven nonpolar narcotic chemicals to the cladoceran Ceriodaphnia cf. dubia was determined. C. cf. dubia was found to be approximately four times more sensitive to these narcotic chemicals than Daphnia magna tested under virtually identical conditions. The toxicity data were also used to develop and validate quantitative structure-activity relationships (QSARs) using a range of physicochemical properties of the chemicals. The three best QSARs, based on octanol-water partition coefficients and two lipid-water partition coefficients, were able to explain 98% of the variation in toxicity. The mean absolute percentage errors between the predicted and experimental EC50 values for these three QSARs were 17.3%, 20.6%, 24.6%. Neither the critical concentration (CC) nor the critical volume (CV) hypotheses validly modeled the toxicity data when octanol-water and triolein-water partition coefficients were used although the CV hypothesis was the better of the two. When a phospholipid-water partition coefficient was used the CV hypothesis was valid. The mean toxic membrane volume fraction of 0.48 x 10(-2) m3/m3 derived in this study agreed with published values for nonpolar narcotics and supports the use of this property to determine the mode of action of chemicals.

Quantitative structure-toxicity relationships for chlorophenols to bioluminescent lux-marked bacteria using atom-based semi-empirical molecular-orbital descriptors.

Literature data on the toxicity of chlorophenols for three luminescent bacteria (Vibrio fischeri, and the lux-marked Pseudomonas fluorescens 10586s pUCD607 and Burkholderia spp. RASC c2 (Tn4431)) have been analyzed in relation to a set of computed molecular physico-chemical properties. The quantitative structure-toxicity relationships of the compounds in each species showed marked differences when based upon semi-empirical molecular-orbital molecular and atom based properties. For mono-, di- and tri-chlorophenols multiple linear regression analysis of V. fischeri toxicity showed a good correlation with the solvent accessible surface area and the charge on the oxygen atom. This correlation successfully predicted the toxicity of the heavily chlorinated phenols, suggesting in V. fischeri only one overall mechanism is present for all chlorophenols. Good correlations were also found for RASC c2 with molecular properties, such as the surface area and the nucleophilic super-delocalizability of the oxygen. In contrast the best QSTR for P. fluorescens contained the 2nd order connectivity index and ELUMO suggesting a different, more reactive mechanism. Cross-species correlations were examined, and between V. fischeri and RASC c2 the inclusion of the minimum value of the nucleophilic susceptibility on the ring carbons produced good results. Poorer correlations were found with P. fluorescens highlighting the relative similarity of V. fischeri and RASC c2, in contrast to that of P. fluorescens.

Examining pain in aggressive cognitively impaired older adults.

Few studies have explored the phenomenon of pain in people with severe cognitive impairment. Pain assessment, which depends primarily on people's ability to describe dimensions of pain, becomes problematic when clients' cognitive impairment is so severe they cannot respond to pain assessment tools. The purpose of this study was to describe the phenomenon of pain for a subgroup of aggressive cognitively impaired nursing home residents who were enrolled in a larger study of aggressive behavior. To determine if pain was a possible factor influencing aggression, information was sought from five sources: family members, nursing assistant (NA) caregivers, medical record listings of pain-related diagnoses, use of analgesics, and observations of aggressive behaviors. Families reported pain in 44% of subjects, while NAs reported pain in 66% of subjects. Seventy-six percent of subjects had one or more pain-causing diagnoses. Sixty-four percent of subjects whose family members thought they may have pain were being treated with analgesics, compared to 44% of subjects whose NA reported they may be experiencing pain. Aggression scores were significantly higher in subjects who had two or more pain-related diagnoses and in subjects with arthritis. Nurses who are aware of a history of pain, reports of pain by families and caregivers, presence of pain-related medical diagnoses, and who realize pain may be a trigger for aggressive behavior may be more likely to recognize pain in cognitively impaired older adults. Better pain assessment should lead to improved treatment of pain in this population.

Managing the cost of documentation: the FACT Charting system.

Nursing managers and staff RNs must work together to manage documentation costs. The FACT Charting system realized one-time savings of approximately $500,000 through the redesign of repetitive, redundant forms and through increased efficiency using flow sheets and concise narrative notes.

Revisions to the derivation of the Australian and New Zealand guidelines for toxicants in fresh and marine waters.

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality are a key document in the Australian National Water Quality Management Strategy. These guidelines released in 2000 are currently being reviewed and updated. The revision is being co-ordinated by the Australian Department of Sustainability, Environment, Water, Population and Communities, while technical matters are dealt with by a series of Working Groups. The revision will be evolutionary in nature reflecting the latest scientific developments and a range of stakeholder desires. Key changes will be: increasing the types and sources of data that can be used; working collaboratively with industry to permit the use of commercial-in-confidence data; increasing the minimum data requirements; including a measure of the uncertainty of the trigger value; improving the software used to calculate trigger values; increasing the rigour of site-specific trigger values; improving the method for assessing the reliability of the trigger values; and providing guidance of measures of toxicity and toxicological endpoints that may, in the near future, be appropriate for trigger value derivation. These changes will markedly improve the number and quality of the trigger values that can be derived and will increase end-users' ability to understand and implement the guidelines in a scientifically rigorous manner.

Field dissipation of 4-nonylphenol, 4-t-octylphenol, triclosan and bisphenol A following land application of biosolids.

The persistence of contaminants entering the environment through land application of biosolids needs to be understood to assess the potential risks associated. This study used two biosolids treatments to examine the dissipation of four organic compounds: 4-nonylphenol, 4-t-octylphenol, bisphenol A and triclosan, under field conditions in South Australia. The pattern of dissipation was assessed to determine if a first-order or a biphasic model better described the data. The field dissipation data was compared to previously obtained laboratory degradation data. The concentrations of 4-nonylphenol, 4-t-octylphenol and bisphenol A decreased during the field study, whereas the concentration of triclosan showed no marked decrease. The time taken for 50% of the initial concentration of the compounds in the two biosolids to dissipate (DT50), based on a first-order model, was 257 and 248 d for 4-nonylphenol, 231 and 75 d for 4-t-octylphenol and 289 and 43 d for bisphenol A. These field DT50 values were 10- to 20-times longer for 4-nonylphenol and 4-t-octylphenol and 2.5-times longer for bisphenol A than DT50 values determined in the laboratory. A DT50 value could not be determined for triclosan as this compound showed no marked decrease in concentration. The biphasic model provided a significantly improved fit to the 4-t-octylphenol data in both biosolids treatments, however, for 4-nonylphenol and bisphenol A it only improved the fit for one treatment. This study shows that the use of laboratory experiments to predict field persistence of compounds in biosolids amended soils may greatly overestimate degradation rates and inaccurately predict patterns of dissipation.

Degradation of 4-nonylphenol, 4-t-octylphenol, bisphenol A and triclosan following biosolids addition to soil under laboratory conditions.

Land application of biosolids is common practice in many countries, however, there are some potential risks associated with the presence of contaminants within the biosolids. This laboratory study examined the degradation of four commonly found organic compounds, 4-nonylphenol, 4-t-octylphenol, bisphenol A, and triclosan, in soil following the addition of two biosolids over 32 weeks. The pattern of degradation was assessed to determine if it followed a standard first-order decay model or if a biphasic model with a degrading and a recalcitrant fraction better described the data. The time taken for the initial concentrations to decrease by 50% (DT50), based on a first-order model, was 12-25 d for 4-nonylphenol, 10-14 d for 4-t-octylphenol, 18-102 d for bisphenol A, and 73-301 d for triclosan. For 4-nonylphenol, bisphenol A and triclosan, the biphasic model fitted the degradation data better than the first-order model, indicating the presence of a degrading fraction and a non-degrading recalcitrant fraction. The recalcitrant fraction for these three compounds at the completion of the 32 week experiment was 17-21%, 24-42%, and 30-51% of the initial concentrations, respectively. For 4-t-octylphenol, the first-order model was sufficient in explaining the degradation data, indicating that no recalcitrant fraction was present. This study showed that biphasic degradation occurred for some organic compounds in biosolids amended soil and that the use of standard first-order degradation models may underestimate the persistence of some organic compounds following land application of biosolids.