Environmental fate and toxicology of clomazone.

Clomazone, an isoxazolane herbicide, was first registered for use in 1986 for pest grasses and broad leaf weeds. Although the exact mode of action is still unclear, it is well documented that clomazone causes bleaching of foliar structures; the clomazone metabolite 5-ketoclomazone is regarded to cause the bleaching and to be the ultimate plant toxicant. Although clomazone exhibits low mammalian toxicity and is selective towards certain plant species, studies have shown that it does inhibit AChE and catalase activities. In addition, it has been found to be highly toxic to aquatic invertebrates, in particular mysid shrimp.Clomazone has a low Henry's law constant and moderate vapor pressure, and thus may volatilize from dry soils. Photolysis represents a minor dissipationpathway; however, clomazone can be photolytically degraded under both direct and indirect conditions. Clomazone has high water solubility, and it is often assumed to undergo hydrolysis easily; unfortunately, this is not the case. Clomazone is stable over a wide pH range and does not hydrolyze. Clomazone has a weak to moderates oil adsorption coefficient; therefore, its affinity to sorb to soil is minimal, rendering it a potential threat to groundwater supplies.Microbial metabolism is the major degradation pathway, resulting in products such as 5-hydroxyclomazone, hydroxymethylclomazone, 2-chlorobenzyl alcohol and 3'-hydroxyclomazone. Although clomazone has not been shown to degrade viahydrolysis, it nonetheless represents a potential threat to aquatic organisms. With this in mind, caution should be taken when applying clomazone or when draining fields that have detectable clomazone residues.

Environmental fate and toxicology of chlorothalonil.

Chlorothalonil is a broad spectrum, non systemic, organochlorine pesticide that was first registered in 1966 for turf grasses, and later for several food crops. Chlorthalonil has both a low Henry's law constant and vapor pressure, and hence, volatilization losses are limited. Although, chlorothalonil's water solubility is low, studies have shown it to be highly toxic to aquatic species. Mammalian toxicity (to rats and mice) is moderate, and produces adverse effects such as, tumors, eye irritation and weakness. Although, there is no indication that chlorothalonil is a human carcinogen,there is sufficient evidence from animal studies to classify it as a probable carcinogen.Chlorothalonil has a relatively low water solubility and is stable to hydrolysis.However, hydrolysis under basic conditions may occur and is considered to be a minor dissipation pathway. As a result of its high soil adsorption coefficient this fungicide strongly sorbs to soil and sediment. Therefore, groundwater contamination is minimal. Degradation via direct aqueous or foliar photolysis represents a major dissipation pathway for this molecule, and the photolysis rate is enhanced by natural photosensitizers such as dissolved organic matter or nitrate. In addition to photolysis, transformation by aerobic and anaerobic microbes is also a major degradation pathway. Under anaerobic conditions, hydrolytic dechlorination produces the stable metabolite 4-hydroxy-2,5,6-trichloroisophthalonitrile. Chlorothalonil is more efficiently degraded under neutral pH conditions and in soil containing a low carbon content.

Methods for deriving pesticide aquatic life criteria for sediments.

In this review, we evaluated three main current approaches for deriving sediment quality guidelines: empirical, mechanistic (equilibrium partitioning), and spiked sediment toxicity testing approaches. Empirical approaches determine ranges of sediment concentrations that are likely or unlikely to cause toxicity, based on large datasets of matching sediment chemistry, field, and laboratory toxicity data. The empirical approaches are not suitable for determining SQC for specific pesticides because (I) direct cause-effect relationships between single sediment contaminants and toxicity cannot be discerned; (2) chemistry measurements have not accounted for bioavailability, which leads to numeric values with high uncertainty and low reliability; and (3) for many pesticides, little or no matching chemistry and toxicity data are available. In the EqP approach, SQC are derived by entering existing aquatic toxicity data into the equilibrium-partitioning model. This approach is practical for pesticides with water quality criteria in place, but the assumption of equilibrium in aquatic ecosystems is questionable, and the EqP approach neglects available sediment toxicity data. The SSTT approaches utilize sediment toxicity data, creating a scientifically defensible foundation for SQC, but experimental uncertainties regarding spiking technique and equilibration times are yet to be eliminated. The species sensitivity distribution approach generates criteria with confidence intervals, providing a measure of uncertainty, but requires relatively large datasets, whereas the assessment factor method lacks quantification of uncertainty but only requires few data to calculate conservative criteria. Several existing methodologies incorporate a combination of approaches that is dependent on data availability and the physicochemical properties of the compound of interest.A summary of the differences and similarities between key elements of the seven methodologies emphasized in this review is displayed in Table 6. One important element regarding sediment contamination is the incorporation of bioavailability and multiple exposure routes, which must be addressed to achieve a technically defensible methodology. It is crucial that bioavailability be incorporated in both criteria derivation and compliance determination (sampling) to ensure that data are comparable. Recent research on bioavailability of sediment contaminants has indicated that the freely dissolved pore water fraction corresponds well with uptake and toxicity. For species having significant exposure via ingestion of contaminated food and/or sediments and/or direct sediment contact, exposure may be underpredicted if these additional exposure routes are overlooked. Future SQC methodologies will be greatly improved by accounting for factors relevant for bioavailability and exposure pathways. To develop a completely new methodology, existing methodologies offer valuable building blocks that are well suited for adaptation. A new method will be more reliable and robust if it utilizes more refined risk assessments than currently are available in existing methodologies. To date, the most comprehensive methodologies for deriving single numeric SQC are those of the Netherlands and the EU,which include both SSTT and EqP approaches.

Environmental fate and toxicology of methomyl.

The insecticide methomyl, an oxime carbamate, was first introduced in 1968 for broad spectrum control of several insect classes, including Lepidoptera, Hemiptera, Homoptera, Diptera, and Coleoptera. Like other carbamates, it inhibits AChE activity, resulting in nerve and/or tissue failure and possibly death. Considered highly toxic to insects (larval and adult stages), methomyl is thought to be metabolically degraded via mixed-function oxidase(s). Methomyl has both a low vapor pressure and Henry's law constant; hence, volatilization is not a major dissipation route from either water or moist or dry soils. Photolysis represents a minor dissipation pathway; however, under catalytic conditions, degradation via photolysis does occur. Methomyl possesses a moderate-to-high water solubility; thus hydrolysis, under alkaline conditions, represents a major degradation pathway. Methomyl has a low-to-moderate sorption capacity to soil. Although results may vary with soil type and organic matter content, methomyl is unlikely to persist in complex soils. Methomyl is more rapidly degraded by microbes, and bacterial species have been identified that are capable of using methomyl as a carbon and/or nitrogen source. The main degradation products of methomyl from both abiotic and biotic processes are methomyl oxime, acetonitrile, and CO2. Methomyl is moderately to highly toxic to fishes and very highly toxic to aquatic invertebrates. Methomyl is highly toxic orally to birds and mammals. Methomyl is classed as being highly toxic to humans via oral exposures, moderately toxic via inhalation, and slightly toxic via dermal exposure. At relatively high doses, it can be fatal to humans. Although methomyl has been widely used to treat field crops and has high water solubility, it has only infrequently been detected as a contaminant of water bodies in the USA. It is classified as a restricted-use insecticide because of its toxicity to multiple nontarget species. To prevent nontarget species toxicity or the possibility of contamination, as with all pesticides, great care should be taken when applying methomyl-containing products for agricultural, residential, or other uses.

Aquatic life water quality criteria derived via the UC Davis method: II. Pyrethroid insecticides.

Aquatic life water quality criteria were derived for five pyrethroids using a new methodology developed by the University of California, Davis (TenBrook et al.2010). This methodology was developed to provide an updated, flexible, and robust water quality criteria derivation methodology specifically for pesticides. To derive the acute criteria, log-logistic SSDs were fitted to the medium-sized bifenthrin,cyfluthrin, and cypermethrin acute toxicity data sets while the X-cyhalothrin and permethrin acute data sets were larger, and Burr Type III SSDs could be fitted to these data sets. A review of the cyfluthrin acute criterion revealed that it was not protective of the most sensitive species in the data set, H. azteca, so the acute value was adjusted downward to calculate a more protective criterion. Similarly, the cypermethrin criteria were adjusted downward to be protective of H. azteca.Criteria for bifenthrin, X-cyhalothrin, and permethrin were calculated using the median fifth percentile acute values while the cyfluthrin and cypermethrin criteria were calculated with the next lowest acute value (median first percentile). Chronic data sets were limited in all cases, so ACRs were used for chronic criteria calculations, instead of statistical distributions. Sufficient corresponding acute and chronic data were not available for bifenthrin, cypermethrin, or permethrin, so a default ACR was used to calculate these chronic criteria while measured ACRs were used for cyfluthrin and X-cyhalothrin. A numeric scoring system was used to sort the acute and chronic data, based on relevance and reliability, and the individual study scores are included in the Supporting Information.According to the USEPA (1985) method, the data sets gathered for these five pyrethroids would not be sufficient to calculate criteria because they were each missing at least one of the eight taxa required by that method. The USEPA (1985)method generates robust and reliable criteria, and the goal of creating the UCDM was to create a method that also yields statistically robust criteria, but with more flexible calculation methods to accommodate pesticide data sets of varied sizes and diversities. Using the UCDM, acute and chronic water quality criteria were derived for bifenthrin (4 and 0.6 ng/L, respectively), cyfluthrin (0.3 and 0.05 ng/L, respectively), cypermethrin (1 and 0.2 ng/L, respectively), X-cyhalothrin (1 and 0.5 ng/L,respectively), and permethrin (10 and 2 ng/L, respectively). Water quality criteria for these five pyrethroids can be used by environmental managers to control the increasing problem of surface water contamination by pesticides.

Aquatic life water quality criteria derived via the UC Davis method: I. Organophosphate insecticides.

A new methodology for deriving freshwater aquatic life water quality criteria,developed by the University of California Davis, was used to derive criteria for three organophosphate insecticides. The UC Davis methodology resulted in similar criteria to other accepted methods, and incorporated new approaches that enable criteria generation in cases where the existing USEPA guidance cannot be used.Acute and chronic water quality criteria were derived for chlorpyrifos (10 and 10 ng/L, respectively), diazinon (200 and 70 ng/L, respectively), and malathion(170 and 28 ng/L, respectively). For acute criteria derivation, Burr Type III SSDs were fitted to the chlorpyrifos and diazinon acute toxicity data sets while an alternative assessment factor procedure was used for malathion because that acute data set did not contain adequate species diversity to use a distribution.ACRs were used to calculate chronic criteria because there was a dearth of chronic data in all cases, especially for malathion, for which there was a lack of paired acute and chronic invertebrate data. Another alternate procedure enabled calculation of the malathion chronic criterion by combining a default ratio with the experimentally derived ratios. A review of the diazinon chronic criterion found it to be under protective of cladoceran species, so a more protective criterion was calculated using a lower distributional estimate. The acute and chronic data sets were assembled using a transparent and consistent system for judging the relevance and reliability of studies, and the individual study review notes are included.The resulting criteria are unique in that they were reviewed to ensure particular protection of sensitive and threatened and endangered species, and mixture toxicity is incorporated into criteria compliance for all three compounds.For chlorpyrifos and diazinon, the UCDM generated criteria similar to the long-standing USEPA (1985) method, with less taxa requirements, a more statistically robust distribution, and the incorporation of new advances in risk assessment and ecotoxicology. According to the USEPA (1985) method, the data set gathered for malathion would not be sufficient to calculate criteria because it did not contain data for a benthic crustacean. Benthic crustacean data is also required to use a distributional calculation method by the UCDM, but when data is lacking the UCDM provides an alternate calculation method." The resulting criteria are associated with higher, unquantifiable uncertainty, but they are likely more accurate than values generated using static safety factors, which are currently common in risk assessment.

NMR-based characterization of the acute metabolic effects of weathered crude and dispersed oil in spawning topsmelt and their embryos.

Oil spill responders require information on the relative toxicity of dispersed and un-dispersed oil in order to make informed decisions regarding the use of chemical dispersants during spill events. Toxicity of the water-accommodated fraction (WAF) and the chemically-enhanced WAF (CEWAF; via the dispersant Corexit 9500) of weathered Prudhoe Bay crude oil was investigated using adult and embryonic topsmelt; topsmelt are an ecologically important atherinid in California bays and estuaries and an important indicator species. Following 96-h exposures, metabolite profiles were measured using 1D (1)H nuclear magnetic resonance (NMR) spectroscopy and compared via principal component analysis. Similar metabolic profiles were obtained between WAF- and CEWAF-exposed adults and embryos. Although metabolic changes, for the adults lacked significance, significant increasing and decreasing metabolic changes were observed for embryos directly exposed. Furthermore, no mortality was observed for embryos, exposed to WAF and normal development occurred, whereas CEWAF exposed embryos lead to mortality and cardiovascular abnormalities. Observed toxicological information, specifically for developing fish, can aide resource managers in the relative risk of treating oil spills with dispersant.

Differential oxidative metabolism and 5-ketoclomazone accumulation are involved in Echinochloa phyllopogon resistance to clomazone.

Echinochloa phyllopogon (late watergrass) is a major weed of California rice (Oryza sativa) that has evolved cytochrome P450-mediated metabolic resistance to different herbicides with multiple modes of action. E. phyllopogon populations from Sacramento Valley rice fields have also recently shown resistance to the herbicide clomazone. Clomazone is a proherbicide that must be metabolized to 5-ketoclomazone, which is the active compound that inhibits deoxyxylulose 5-phosphate synthase, a key enzyme of the nonmevalonate isoprenoid pathway. This study evaluated the differential clomazone metabolism within strains of the same species to investigate whether enhanced oxidative metabolism also confers clomazone resistance in E. phyllopogon. Using reverse-phase liquid chromatography-tandem mass spectrometry techniques in the multireaction monitoring mode, we elucidated that oxidative biotransformations are involved as a mechanism of clomazone resistance in this species. E. phyllopogon plants hydroxylated mostly the isoxazolidinone ring of clomazone, and clomazone hydroxylation activity was greater in resistant than in susceptible plants. The major clomazone metabolites resulted from monohydroxylation and dihydroxylation of the isoxazolidinone ring. Resistant plants accumulated 6- to 12-fold more of the monohydroxylated metabolite than susceptible plants, while susceptible plants accumulated 2.5-fold more of the phytotoxic metabolite of clomazone, 5-ketoclomazone. Our results demonstrate that oxidative metabolism endows multiple-herbicide-resistant E. phyllopogon with cross-resistance to clomazone through enhanced herbicide degradation and lower accumulation of the toxic metabolite in resistant versus susceptible plants.

Metabolic responses produced by crude versus dispersed oil in Chinook salmon pre-smolts via NMR-based metabolomics.

Crude oil spills from tankers remain a serious threat along coastal California. Resource managers require information on the acute toxicity of treated and untreated oil, and their sublethal effects on wildlife. This investigation compared the toxic actions of the water-accommodated fraction (WAF) and the chemically-enhanced WAF (CEWAF; Corexit 9500) of Prudhoe Bay crude oil in pre-smolt Chinook salmon (Oncorhynchus tshawytscha) via nuclear magnetic resonance (NMR)-based metabolomics. Metabolite profiles from muscle samples, after 96h exposures, were measured using 1D (1)H NMR and compared via principal component analysis. It was determined that both WAF and CEWAF produced similar profiles in which amino acids, lactate and ATP comprised the highest intensity signals. Overall, metabolic substrates and growth measurements did not show residual effects of short-term exposure on long-term development. In conclusion, the 96h LC(50)s indicate dispersant application significantly decreased hydrocarbon potency and identified metabolites may be bio-indicators of hydrocarbon stress from hydrocarbon exposure.

Quantum Yield for the Aqueous Photochemical Degradation of Chlorantraniliprole and Simulation of Its Environmental Fate in a Model California Rice Field.

The photochemical degradation of chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)phenyl]-1-(3-chloro-2-pyridine-2-yl)-1H-pyrazole-5-carboxamide; CAP) was characterized under simulated solar light with 2-nitrobenzaldehyde (2NB) actinometry. Overall, aqueous CAP degraded quickly via direct photodegradation with no significant difference observed between high-purity water and filtered rice field water. The 24-h average half-life normalized to summer sunlight using 2NB was 34.5 ± 4.0 h (jCAP,env = 0.020 ± 0.0023 h-1 , n = 3), and the calculated apparent quantum yield in simulated sunlight was 0.0099 ± 0.00060. These new values were used-alongside previously characterized data for air/and soil/water partitioning, degradation in soil, and hydrolysis-in the Pesticides in Flooded Applications Model to simulate CAP dissipation in a model California (USA) rice field. The model estimates an environmental half-life of 26 d in the aqueous phase, but the bulk of applied CAP remains in the benthic zone and degrades, with estimated half-lives of 29 and 92 d in flooded and drained fields, respectively. Environ Toxicol Chem 2020;39:1929-1935. © 2020 SETAC.

Methods for deriving pesticide aquatic life criteria.

Environmental regulators charged with protecting water quality must have scientifically defensible water quality goals. For protection of aquatic life, regulators need to know what levels of contaminants a water body can tolerate, without producing adverse effects. The USEPA has developed water quality criteria for many chemicals, but few are for current-use pesticides. Other countries also derive aquatic life criteria utilizing a variety of methodologies. As a prelude to developing a new criteria derivation methodology, this chapter explores the current state of aquatic life criteria derivation around the world. Rather than discussing each methodology independently, this review is organized according to critical elements that must be part of a scientifically defensible methodology. All of the reviewed methodologies rely on effects data to derive aquatic life criteria. Water quality criteria may be derived from single-species toxicity data by statistical extrapolation procedures (for adequate data sets), or by use of empirically based AFs (for data sets of any size). Assessment factor methods are conservative and have a low probability of underestimating risk, with a concomitant high probability of overestimating risk. Extrapolation methods may also under-, or overestimate risk, but uncertainty is quantifiable and is reduced when larger data sets are used. Although less common, methods are also available for criteria derivation using multispecies toxicity data. Environmental toxicity of chemicals is affected by several factors. Some of these factors can be addressed in criteria derivation, and some cannot. For example, factors such as magnitude, duration and frequency of exposure may be incorporated into criteria, either through use of time-to-event and population models or by derivation of both acute and chronic criteria that have duration and frequency components. Aquatic species may be exposed to hydrophobic organic chemicals by multiple routes. They may take up residues directly from water, or may be exposed dietarily, or combinations of both. Unfortunately, to properly address such multiple routes in criteria derivation, food web models are needed that work for chemicals that have specific modes of action. Similarly, both bioavailability and toxicity parameters may contribute to derivation of criteria, providing sufficient data are available. Ecotoxicological effects and physical-chemical data are needed for criteria derivation. The quality and quantity of required data are clearly stated in existing methodologies; some guidelines provide very specific data quality requirements. The level of detail provided by guidelines varies among methodologies. Most helpful are those that provide lists of acceptable data sources, descriptions of adequate data searches, schemes for rating ecotoxicity data, specifications of required data types (e.g., acute vs chronic), and instructions for data reduction. Many methodologies present procedures for deriving criteria from both large and small data sets. Very small data sets may be supplemented through the use of QSARs for selected pesticides, and through the use of models such as ICE (for prediction of toxicity to under-tested species), and ACE (for estimation of chronic toxicity from acute data). The toxicity of mixtures is addressed by several existing methodologies. In some cases, additional AFs are applied to criteria to account for exposure to mixtures, whereas in others, concentration addition models are used to assess compliance. Multiple stressors and bioaccumulation are also addressed in some methodologies, by providing for application of additional safety factors. Methods are also available for translating dietary exposure limits for humans or other fish-eating animals into water concentrations. Options for addressing the safety of TES exist, and rely heavily on data from surrogate species to derive criteria. Utilizing partition coefficients, criteria may be harmonized across media to ensure that levels set to protect one compartment do not result in unacceptable levels in other compartments. Several methodologies derive criteria from entire data sets through the use of statistical extrapolations; other methods utilize only the lowest (most sensitive) data point or points. Utilization of entire data sets allows derivation of confidence limits for criteria, and encourages data generation. Criteria derivation methodologies have improved over the past two decades as they have incorporated more ecological risk assessment techniques. No single existing methodology is ideal, but elements of several may be combined, and when used with newer risk assessment tools, will produce more usable and flexible criteria derivation procedures that are protective.

Optimization and validation of a California halibut environmental estrogen bioassay using a heterologous ELISA.

Vitellogenin, the estrogen-inducible yolk protein precursor, serves as an indicator of exposure to estrogen mimicking environmental contaminants. An ELISA for the measurement of California halibut plasma vitellogenin was optimized and validated using a commercially-available antibody developed for another flatfish species, turbot. Attempts to enhance assay performance by addition of a biotinylated antibody, polyethylene glycol, and Tween-20, and altering the preincubation step are described. Inclusion of overnight preincubation was critical for low detection limits. Increasing the amount of Tween-20 to 0.05% in buffers was most effective in achieving accurate quantification of spiked plasma samples. At the IC50, the average recovery of spiked plasma samples was 104% and the interplate CV was 12%. The working range of the assay was 33-1000 ng/mL, while the detection limit in a plasma sample is 2.2 microg/mL. The performance of this assay compared very well to a homologous assay demonstrating that commercially-available antibodies can facilitate the development of bioassays for local environmentally-relevant species. The dose response relationship of halibut Vg to the model compounds 17beta-estradiol and pnonylphenol show that it is a suitable model for further studies of estrogen mimicking contaminants.

Reduction of vitellogenin synthesis by an aryl hydrocarbon receptor agonist in the white sturgeon (Acipenser transmontamus).

Migrating white sturgeon (Acipenser transmontamus) may be subject to agricultural, municipal, and industrial wastewater effluents that likely contain different classes of endocrine-disrupting contaminants. Concern is mounting about the negative effects of environmental estrogens on fish reproduction; however, in environmental mixtures, the affects from estrogenic compounds may be suppressed by aryl hydrocarbon receptor (AhR) ligands. Indeed, reductions in 17beta-estradiol-induced (0.01 and 1 mg/kg) vitellogenin (VTG) levels were observed in white sturgeon coinjected with beta-naphthoflavone (BNF; 50 mg/kg), a model for contaminants that activate the AhR. Variation in the time of injection was used to attempt to correlate VTG inhibition to ethoxyresorufin-O-deethylase activity. No evidence was found to suggest that the inhibition of VTG is a direct result of enhanced estrogen metabolism by BNF-induced enzymes. Results of the present study are relevant for monitoring programs that measure VTG, because these results show that AhR-active environmental contaminants can repress VTG synthesis, which commonly is used as an indicator of estrogen-mimicking contaminants. Furthermore, suppression of natural estrogen signaling by AhR agonists may have significant effects on fish reproduction.

Influence of Flooding, Salinization, and Soil Properties on Degradation of Chlorantraniliprole in California Rice Field Soils.

Chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)phenyl]-1-(3-chloro-2-pyridine-2-yl)-1H-pyrazole-5-carboxamide; CAP) was granted supplemental registration for use in rice cultivation in California through December, 2018. Previous work investigated the partitioning of CAP in California rice field soils; however, its degradation in soils under conditions relevant to California rice culture has not been investigated. The degradation of CAP in soils from two California rice fields was examined under aerobic and anaerobic conditions with varying salinity via microcosm experiments. Results indicate that soil properties governing bioavailability may have a greater influence on degradation than flooding practices or field salinization over a typical growing season. Differences between native and autoclaved soils (t1/2 = 59.0-100.2 and 78.5-171.7 days) suggest that biological processes were primarily responsible for CAP degradation; however, future work should be done to confirm specific biotic processes as well as to elucidate abiotic processes, such as degradation via manganese oxides and formation of nonextractable residues, which may contribute to its dissipation.

Influence of pH and Divalent Metals Relevant to California Rice Fields on the Hydroxide-Mediated Hydrolysis of the Insecticide Chlorantraniliprole.

The hydrolysis of chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)phenyl]-1-(3-chloro-2-pyridine-2-yl)-1H-pyrazole-5-carboxamide; CAP) was investigated over the pH range of 6-10, reflective of California rice field conditions, with variable additions of Cu2+, Zn2+, Mn2+, or Ni2+. Dissipation accelerated as pH increased with half-lives ranging from 26.9 to 2.2 days with slight inhibition in rice field water. The addition of divalent metals was not observed to catalyze the hydrolysis of CAP at pH 6, indicating that the insecticide is likely to remain recalcitrant to hydrolysis in neutral or acidic surface waters. However, Mn2+ and Ni2+ were observed to inhibit hydrolysis at pH 8 and 9. Attenuated total reflectance Fourier transform infrared analysis supports the conclusion that divalent metals may withdraw electron density from the amide nitrogen via interaction with the amide oxygen, though additional quantum chemical modeling is necessary to provide further mechanistic insights. Overall, the hydrolysis of CAP in California rice fields and their surrounding surface waters will be dominated by pH and inhibited by dissolved metal species.

Road proximity increases risk of skeletal abnormalities in wood frogs from National Wildlife Refuges in Alaska.

BACKGROUND: Skeletal and eye abnormalities in amphibians are not well understood, and they appear to be increasing while global populations decline. Here, we present the first study of amphibian abnormalities in Alaska. OBJECTIVE: In this study we investigated the relationship between anthropogenic influences and the probability of skeletal and eye abnormalities in Alaskan wood frogs (Rana sylvatica). METHODS: From 2000 to 2006, we examined 9,269 metamorphic wood frogs from 86 breeding sites on five National Wildlife Refuges: Arctic, Innoko, Kenai, Tetlin, and Yukon Delta. Using road proximity as a proxy for human development, we tested relationships between skeletal and eye abnormalities and anthropogenic effects. We also examined a subsample of 458 frogs for the trematode parasite Ribeiroia ondatrae, a known cause of amphibian limb abnormalities. RESULTS: Prevalence of skeletal and eye abnormalities at Alaskan refuges ranged from 1.5% to 7.9% and were as high as 20% at individual breeding sites. Proximity to roads increased the risk of skeletal abnormalities (p = 0.004) but not eye abnormalities. The only significant predictor of eye abnormalities was year sampled (p = 0.006). R. ondatrae was not detected in any Alaskan wood frogs. CONCLUSIONS: Abnormality prevalence at road-accessible sites in the Kenai and Tetlin refuges is among the highest reported in the published literature. Proximity to roads is positively correlated with risk of skeletal abnormalities in Alaskan wood frogs.

Proteomic identification, cDNA cloning and enzymatic activity of glutathione S-transferases from the generalist marine gastropod, Cyphoma gibbosum.

Glutathione S-transferases (GST) were characterized from the digestive gland of Cyphoma gibbosum (Mollusca; Gastropoda), to investigate the possible role of these detoxification enzymes in conferring resistance to allelochemicals present in its gorgonian coral diet. We identified the collection of expressed cytosolic Cyphoma GST classes using a proteomic approach involving affinity chromatography, HPLC and nano-spray liquid chromatography-tandem mass spectrometry (LC-MS/MS). Two major GST subunits were identified as putative mu-class GSTs; while one minor GST subunit was identified as a putative theta-class GST, apparently the first theta-class GST identified from a mollusc. Two Cyphoma GST cDNAs (CgGSTM1 and CgGSTM2) were isolated by RT-PCR using primers derived from peptide sequences. Phylogenetic analyses established both cDNAs as mu-class GSTs and revealed a mollusc-specific subclass of the GST-mu clade. These results provide new insights into metazoan GST diversity and the biochemical mechanisms used by marine organisms to cope with their chemically defended prey.

Chemistry and fate of triazolopyrimidine sulfonamide herbicides.

The triazolopyrimidine sulfonamide (TSA) herbicides were registered in the United States in 1993. Their mode of action is by inhibition of acetolactate synthase (ALS), an enzyme common to plants and microorganisms but not found in animals. ALS inhibitors include other herbicide families such as the sulfonylureas, imidazolinones, and pyrimidinyl thiobenzoates. In the 1970s, sulfonylureas were the first ALS inhibitors to be introduced to the market. Their discovery was greeted as a great achievement because of their ability to suppress weeds at extremely low application rates compared to previously used herbicides and with low toxicity risk to humans and wildlife. By 1991, the market value of ALS inhibitors had reached $1.3 billion (U.S.). However, some of the problems associated with their use include the induction of resistance in weed species to both ALS-inhibiting and alternative herbicides. ALS inhibitors have also been found to damage nontarget plants at residual levels that are below the detection limits of standard analytical methods (Saari et al. 1994; Whitcomb 1999).