In vivo acetylcholinesterase inhibition, metabolism, and toxicokinetics of aldicarb in channel catfish: role of biotransformation in acute toxicity

A comparative study of enzymatic and immunological parameters in Planorbarius corneus and Biomphalaria glabrata exposed to the organophosphate chlorpyrifos

This study aimed to investigate the acute effects of chlorpyrifos on biomarkers related to neurotoxicity and immunotoxicity in two allopatric freshwater gastropod species belonging to the family Planorbidae. For this purpose, Planorbarius corneus and Biomphalaria glabrata were exposed to chlorpyrifos (active ingredient or commercial formulation) for 48 h at environmentally realistic concentrations (1 and 7.5 μg L^-1). Basal acetylcholinesterase activity in soft tissues and hemolymph was almost one order of magnitude higher in P. corneus than in B. glabrata. However, upon chlorpyrifos exposure, statistically significant inhibition of enzymatic activity was registered in both species. Acetylcholinesterase was more sensitive to inhibition in soft tissues than in hemolymph. The highest inhibition was observed in the B. glabrata soft tissues exposed to the commercial formulation (88 % at 1 μg L^-1 and 93 % at 7.5 μg L^-1). Hemocyte number and lysosomal membrane stability did not show significant changes with respect to controls in any of the exposed groups. Superoxide anion generation was diminished (21-46 %) in P. corneus hemocytes exposed to the active ingredient and in B. glabrata hemocytes exposed to the active ingredient or the formulation. In contrast, hemocyte phagocytic activity increased in all exposed groups. Phagocytosis was most stimulated (89 %) in hemocytes sampled from B. glabrata treated with 7.5 μg L^-1 chlorpyrifos. Altogether the results suggest that the freshwater gastropods P. corneus and B. glabrata are suitable model animals for environmental monitoring studies in the Northern Hemisphere and Latin America, respectively. Furthermore, these results add information on the relevance of testing pesticide formulations and on the usefulness of acetylcholinesterase inhibition and immunological parameters as biomarkers of the acute effects of chlorpyrifos in these species.

Comparison of Lindane and Carbaryl Pesticide Bioaccumulation in the Common Sole (Solea solea)

Organochlorines and carbamates are common pesticides predominantly employed in agriculture. Large amounts of pesticides make their way into rivers and marine habitats. They accumulate in aquatic organisms through different exposure routes and gradually move up the food chain. Since contaminant bioaccumulation in animals is affected by several factors, this work harnessed several different approaches to explore the persistence of lindane, a long banned organochlorine pesticide, and carbaryl, a newer generation pesticide, in common sole (Solea solea), a major commercial species in Adriatic fisheries. Lindane was not only more accumulated than carbaryl in sole liver, but it was also detected in greater amount in muscle tissue, the edible part (lindane, 7 ± 4 ng/g; carbaryl, <0.004 ng/g w/w). Additional assays documented a greater accumulation of lindane in adults compared with juveniles and in specimens caught offshore than in those collected close to the coast. The present findings demonstrate the different accumulation dynamics of the two pesticides to confirm the benefits derived from the replacement of organochlorine pesticides with carbamate compounds.

Acetylcholinesterase in zebrafish embryos as a tool to identify neurotoxic effects in sediments

In order to clarify the suitability of zebrafish (Danio rerio) embryos for the detection of neurotoxic compounds, the acetylcholinesterase assay was adapted and validated with a series of priority pollutants listed as relevant for the European water policy (Aroclor 1254, 2,3-benzofuran, bisphenol A, chlorpyrifos, paraoxon-methyl, quinoline, and methyl mercury chloride) as well as acetonic extracts from three sediments of known contamination. The acute toxicities of the model substances and the sediment extracts were determined by means of the fish embryo test as specified in OECD TG 236, and concentrations as low as the effective concentration at 10% inhibition (EC10) were used as the highest test concentration in the acetylcholinesterase test in order to avoid nonspecific systemic effects mimicking neurotoxicity. Among the model compounds, only the known acetylcholinesterase inhibitors paraoxon-methyl and chlorpyrifos produced a strong inhibition to about 20 and 33%, respectively, of the negative controls. For the sediment extracts, a reduction of acetylcholinesterase activity to about 60% could only be shown for the Vering Canal sediment extracts; this could be correlated to high contents of acetylcholinesterase-inhibiting polycyclic aromatic hydrocarbons (PAHs) as identified by chemical analyses. Co-incubation of the Vering Canal sediment extracts with chlorpyrifos at EC10 concentrations each did not significantly increase the inhibitory effect of chlorpyrifos, indicating that the mode of action of acetylcholinesterase inhibition by the sediment-borne PAHs is different to that of the typical acetylcholinesterase blocker chlorpyrifos. Overall, the study documents that zebrafish embryos represent a suitable model not only to reveal acetylcholinesterase inhibition, but also to investigate various modes of neurotoxic action.

Effects of salinity acclimation on the expression and activity of Phase I enzymes (CYP450 and FMOs) in coho salmon (Oncorhynchus kisutch)

Phase I biotransformation enzymes are critically important in the disposition of xenobiotics within biota and are regulated by multiple environmental cues, particularly in anadromous fish species. Given the importance of these enzyme systems in xenobiotic/endogenous chemical bioactivation and detoxification, the current study was designed to better characterize the expression of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch) and the effects of salinity acclimation on those enzymes. Livers, gills, and olfactory tissues were collected from coho salmon (O. kisutch) after they had undergone acclimation from freshwater to various salinity regimes of seawater (8, 16 and 32 g/L). Using immunoblot techniques coupled with testosterone hydroxylase catalytic activities, 4 orthologs of cytochrome P450 (CYP1A, CYP2K1, CYP2M1, and CYP3A27) were measured in each tissue. Also, the expression of 2 transcripts of flavin-containing monooxygenases (FMO A and B) and associated activities were measured. With the exception of CYP1A, which was down-regulated in liver, protein expression of the other 3 enzymes was induced at higher salinity, with the greatest increase observed in CYP2M1 from olfactory tissues. In liver and gills, 6β- and 16β-hydroxylation of testosterone was also significantly increased after hypersaline acclimation. Similarly, FMO A was up-regulated in all 3 tissues in a salinity-dependent pattern, whereas FMO B mRNA was down-regulated. FMO-catalyzed benzydamine N-oxygenase and methyl p-tolyl sulfoxidation were significantly induced in liver and gills by hypersalinity, but was either unchanged or not detected in olfactory tissues. These data demonstrate that environmental conditions may significantly alter the toxicity of environmental chemicals in salmon during freshwater/saltwater acclimation.

Investigation of neurotoxic and immunotoxic effects of some plant growth regulators at subacute and subchronic applications on rats

The present study was aimed to investigate the effects of subacute and subchronic treatment of some plant growth regulators (PGRs), such as abscisic acid (ABA) and gibberellic acid (GA3), on neurological and immunological biomarkers in various tissues of rats. The activities of acetylcholinesterase (AChE) and butrylcholinesterase (BChE) were selected as biomarkers for neurotoxic biomarkers. Adenosine deaminase (ADA) and myeloperoxidase (MPO) were measured as indicators for immunotoxic investigation purpose. Wistar albino rats were orally administered with 25 and 50 ppm of PGRs ad libitum for 25-50 days continuously with drinking water. The treatment of PGRs caused different effects on the activities of enzymes. Results showed that the administrations of ABA and GA3 increased AChE and BChE activities in some tissues of rats treated with both the dosages and periods of ABA and GA3. With regard to the immunotoxic effects, ADA activity fluctuated, while MPO activity increased after subacute and subchronic exposure of treated rat tissues to both dosages when compared with the controls. The observations presented led us to conclude that the administrations of PGRs at subacute and subchronic exposure increased AChE, BChE, and MPO activities, while fluctuating the ADA activity in various tissues of rats. This may reflect the potential role of these parameters as useful biomarkers for toxicity of PGRs.

Risks of carbamate and organophosphate pesticide mixtures to salmon in the Pacific Northwest

Salmon populations in the Pacific Northwest are being affected by a variety of environmental stressors including intense fishing pressure, parasites and disease, climatic variability and change, land development, hatchery production, hydropower operations, stormwater runoff, and exposure to toxic contaminants. In recent years, there has been much concern that mixtures of pesticides are causing toxic effects to Pacific salmon. In this study, we compared measured stream water concentrations from 2 monitoring studies conducted in the Pacific Northwest with concentration-response curves derived for inhibition of brain acetylcholinesterase activity in juvenile coho salmon (Oncorhynchus kisutch) for mixtures of organophosphate (OPs) and carbamate (CBs) pesticides. In the first monitoring study, samples were collected from 2003 to 2007 in salmonid-bearing waters of 5 urban or agricultural watersheds in Washington State. This study was targeted to areas of high pesticide use and generally involved weekly sampling during the pesticide use season. The second monitoring study was the United States Geological Survey National Water Quality Assessment that included samples taken from 2003 to 2010 in California, Idaho, Oregon, and Washington. OPs and CBs were frequently detected in both studies. The available monitoring data collected since 2003, however, demonstrates that mixtures of OPs and CBs in surface waters rarely occur at levels capable of producing significant physiological and behavioral effects in Pacific salmon. The observed mixtures never reached concentrations capable of causing mortality. We conclude that mixtures of organophosphates and carbamates do not pose a significant direct risk to Pacific salmon.

Evaluation of the immunity activity of glycyrrhizin in AR mice

In this study, we evaluated effect of glycyrrhizin on immunity function in allergic rhinitis (AR) mice. The AR mice model were induced by dripping ovalbumin in physiological saline (2 mg mL⁻¹, 10 μL) into the bilateral nasal cavities using a micropipette. After the AR model was induced, mice were randomly divided into six groups: the normal control, model, lycopene 20 mg kg⁻¹ (as positive control drug) group, and glycyrrhizin 10, 20, 30 mg kg⁻¹ groups. After the sensitization day 14, lycopene (20 mg/kg BW) and glycyrrhizin (10, 20 and 30 mg/kg BW) were given orally for 20 days once a day. Mice in the normal control and model groups were given saline orally once a day for 20 days. Results showed that glycyrrhizin treatment could dose-dependently significantly reduce blood immunoglobulin E (IgE), interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-6 (IL-6), nitrous oxide (NO), tumor necrosis factor-alpha (TNF-α) levels and nitrous oxide synthase (NOS) activity and enhance blood immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM), interleukin-2 (IL-2) and interleukin-12 (IL-12) levels in AR mice. Furthermore, glycyrrhizin treatment could dose-dependently significantly enhance acetylcholinesterase (AchE) activity and reduce substance P (SP) level in peripheral blood and nasal mucosa of AR mice. We conclude that glycyrrhizin can improve immunity function in AR mice, suggesting a potential drug for the prevention and therapy of AR.

Impacts of climate change on hypersaline conditions of estuaries and xenobiotic toxicity

Climate change has had significant impacts on the hydrologic cycle of the planet. Of particular concern are estuarine environments, such as San Francisco Bay (USA) which is fed by diminishing snow pack runoff leading to gradual increases in salinity. Salinity enhances the acute toxicity of several agricultural chemicals in anadromous fish through augmented biochemical activation catalyzed by enzymes that are induced during hypersaline acclimation. This review discusses the mechanisms of the enhanced toxicity, the enzymes involved and the regulation of the enzymes by hypersaline conditions. Given the rapid changes taking place in the world's waterways, environmental modification of toxicological pathways should be a significant focus of the research community as the toxicity of multiple xenobiotics may be enhanced.

Framework for traits-based assessment in ecotoxicology

A key challenge in ecotoxicology is to assess the potential risks of chemicals to the wide range of species in the environment on the basis of laboratory toxicity data derived from a limited number of species. These species are then assumed to be suitable surrogates for a wider class of related taxa. For example, Daphnia spp. are used as the indicator species for freshwater aquatic invertebrates. Extrapolation from these datasets to natural communities poses a challenge because the extent to which test species are representative of their various taxonomic groups is often largely unknown, and different taxonomic groups and chemicals are variously represented in the available datasets. Moreover, it has been recognized that physiological and ecological factors can each be powerful determinants of vulnerability to chemical stress, thus differentially influencing toxicant effects at the population and community level. Recently it was proposed that detailed study of species traits might eventually permit better understanding, and thus prediction, of the potential for adverse effects of chemicals to a wider range of organisms than those amenable for study in the laboratory. This line of inquiry stems in part from the ecology literature, in which species traits are being used for improved understanding of how communities are constructed, as well as how communities might respond to, and recover from, disturbance (see other articles in this issue). In the present work, we develop a framework for the application of traits-based assessment. The framework is based on the population vulnerability conceptual model of Van Straalen in which vulnerability is determined by traits that can be grouped into 3 major categories, i.e., external exposure, intrinsic sensitivity, and population sustainability. Within each of these major categories, we evaluate specific traits as well as how they could contribute to the assessment of the potential effects of a toxicant on an organism. We then develop an example considering bioavailability to explore how traits could be used mechanistically to estimate vulnerability. A preliminary inventory of traits for use in ecotoxicology is included; this also identifies the availability of data to quantify those traits, in addition to an indication of the strength of linkage between the trait and the affected process. Finally, we propose a way forward for the further development of traits-based approaches in ecotoxicology.

Endosulfan induces changes in spontaneous swimming activity and acetylcholinesterase activity of Jenynsia multidentata (Anablepidae, Cyprinodontiformes)

We assessed changes in spontaneous swimming activity and acetylcholinesterase (AchE) activity of Jenynsia multidentata exposed to Endosulfan (EDS). Females of J. multidentata were exposed to 0.072 and 1.4 microg L(-1) EDS. Average speed and movement percentage were recorded during 48 h. We also exposed females to EDS at five concentrations between 0.072 and 1.4 microg L(-1) during 24 h, and measured the AchE activity in brain and muscle. At 0.072 microg L(-1) EDS swimming motility decreased relative to the control group after 45 h, while at 1.4 microg L(-1) EDS swimming motility decreased after 24 h. AchE activity significantly decreased in muscle when J. multidentata were exposed to EDS above 0.072 microg L(-1), while no significant changes were observed in brain. Thus, changes in swimming activity and AchE activity in muscle are good biomarkers of exposure to EDS in J. multidentata.

Effects of nonylphenol on cholinesterase and carboxylesterase activities in male guppies (Poecilia reticulata)

Compared to the estrogenic effects of 4-nonylphenol (NP), there is little data available on other potential toxic effects of NP in aquatic animals. The effects of NP on cholinesterase (ChE) and carboxylesterase (CbE) activities of male guppies exposed to 10, 60, 150, or 300 μg L(-1) NP were examined after 1, 2, 4, and 7 days of treatment. A significant muscle ChE inhibition, that used acetylthiocholine iodide as a substrate, was noted in male guppies in all NP treatment groups after a 4-day exposure, and 60 and 150 μg L(-1) of NP treatment groups after a 7-day exposure. All guppies exposed to 300 μg L(-1) NP died during the 7-day treatment. However, there was no significant inhibition of muscle ChE that used butyrylthiocholine iodide as a substrate in male guppies for any NP treatments in different exposure times. There were no CbE activity differences in livers of male guppies among NP treatment groups after different exposure times. This is the first report showing the ChE activity inhibition by NP in fish. Further mechanistic studies are needed to define how NP directly or indirectly alters ChE activities at molecular level. The implication of ChE inhibition of NP on potential impacts of aquatic animals also warrants further research.

Muscular and brain cholinesterase sensitivities to azinphos methyl and carbaryl in the juvenile rainbow trout Oncorhynchus mykiss

The organophosphate azinphos methyl (AzMe) and the carbamate carbaryl are the insecticides mostly used in the irrigated valley of Río Negro and Neuquén, Patagonia, Argentina. Juvenile rainbow trout were exposed to AzMe and carbaryl and the sensitivity of skeletal muscular cholinesterase (ChE) and the time course of inhibition and recovery were evaluated. EC50 values demonstrated that AzMe was a stronger in vivo inhibitor of muscular ChE (1.05+/-0.23 microg/L) than carbaryl (270+/-62.23 microg/L). Muscular ChE was significantly less sensitive to both insecticides than brain ChE. EC50 values obtained for muscular ChE were closer than those for brain ChE to the respective pesticide lethal concentrations, pointing out the relevance of the muscular enzyme in determining acute toxicity. The recovery process of ChE activity after carbaryl exposure (500 microg/L) was fast, whereas no significant recovery was observed with AzMe (1 microg/L) after 21 days in uncontaminated media. Brain and muscular ChE were inhibited and showed a significant but not complete recovery after three consecutive 48-h exposures to AzMe (1 microg/L) followed by a recovery period of 7 days. This scheme mimics the periodical application of the insecticides in the region and suggests a certain probability of a sustained ChE inhibition under field conditions, affecting fish development and survival.

Novel view on predicting acute toxicity: decomposing toxicity data in species vulnerability and chemical potency

Chemical risk assessment usually applies empirical methods to predict toxicant effects on different species. We propose a more mechanism-oriented approach, and introduce a method to decompose toxicity data in a contribution from the chemical (potency) and from the exposed species (vulnerability). We use a database for acute aquatic toxicity, and focus on some well-defined chemical classes. Potency is strongly related to hydrophobicity and vulnerability differences between species are small for narcotic compounds. Potencies show less relation with hydrophobicity and interspecies differences are larger for organophosphate- and carbamate insecticides. Photosynthesis inhibitors generally act narcotic to animals, but were more potent for algae. Using these potencies and vulnerabilities, acute toxicity values were well predicted by the proposed approach (within a factor of 3-6). The proposed approach has potential for predicting toxicity for untested species-compound combinations; however, there is a need for a better definition of 'mode of action' in ecotoxicology.

Suborganismic and organismic effects of aldicarb and its metabolite aldicarb-sulfoxide to the zebrafish embryo (Danio rerio)

The new European chemical regulation (REACH) requires a short-term fish test for chemicals where the level of production exceeds 10tons per year. For ethical reasons (3R-concept), an alternative to the acute fish test should be introduced to decrease the number of animal testing with fish. The zebrafish embryo (Danio rerio) test became a valuable tool in ecotoxicology and already replaces the acute fish test for the evaluation of wastewater in Germany. Recent efforts are targeted to use this and other fish embryo tests for the effect assessment of chemicals. The toxic effects of the carbamate insecticide aldicarb and its metabolite aldicarb-sulfoxide to zebrafish embryos were analysed using two approaches with different endpoints. Organismic tests were conducted with zebrafish embryos exposed to the pesticides for 48h. In addition, suborganismic effects were examined analysing the enzyme inhibition of cholinesterases and carboxylesterases. On the organismic level, the only sublethal effect seen was the increase of heart rate at low and decrease at higher concentration with the use of aldicarb-sulfoxide but not with aldicarb (concentration range 0.2-300microM). In contrast, analysis of enzyme inhibitions showed high to very high effects caused by the two carbamates. The enzyme inhibition analysis of whole homogenates of exposed embryos may be advantageous for toxicant screening (biomarker of exposure) and might be used to bridge the gap of sensitivity of the (48h old) zebrafish embryos to adult fish when exposed to anti-cholinesterase substances (biomarker of prospective effect).

In vitro-in vivo extrapolation of quantitative hepatic biotransformation data for fish. I. A review of methods, and strategies for incorporating intrinsic clearance estimates into chemical kinetic models

Scientists studying mammals have developed a stepwise approach to predict in vivo hepatic clearance from measurements of in vitro hepatic biotransformation. The resulting clearance estimates have been used to screen drug candidates, investigate idiosyncratic drug responses, and support chemical risk assessments. In this report, we review these methods, discuss their potential application to studies with fish, and describe how extrapolated values could be incorporated into well-known compartmental kinetic models. Empirical equations that relate extrapolation factors to chemical log K(ow) are given to facilitate the incorporation of metabolism data into bioconcentration and bioaccumulation models. Because they explicitly incorporate the concept of clearance, compartmental clearance-volume models are particularly well suited for incorporating hepatic clearance estimates. The manner in which these clearance values are incorporated into a given model depends, however, on the measurement frame of reference. Procedures for the incorporation of in vitro biotransformation data into physiologically based toxicokinetic (PBTK) models are also described. Unlike most compartmental models, PBTK models are developed to describe the effects of metabolism in the tissue where it occurs. In addition, PBTK models are well suited to modeling metabolism in more than one tissue.

Cholin- and carboxylesterase activities in developing zebrafish embryos (Danio rerio) and their potential use for insecticide hazard assessment

Insecticides are a potential hazard for non-target organisms like fish particularly at run off events. The study of effects to embryos of the zebra fish Danio rerio is already an accepted tool in waste water monitoring, but effects of various groups of substances (like most pesticides) to the zebrafish embryo remain to be studied. Enzymes are often taken as biomarkers of exposure and effect. Therefore cholinesterase isozymes and carboxylesterase were examined for their suitability as biomarkers of insecticide exposure. The activities of cholinesterase and of carboxylesterase were monitored in the first 48 h post-fertilization (hpf) of zebrafish development. Significant specific activities in the range of 0.5-25 U could be measured from the sixth somite stage (12 h) up to the Long Pec stage (48 h) for different cholinesterases using acetyl-, acetyl-beta-methyl-, butyryl- and propionylthiocholin as substrates. The specific activity of carboxylesterase ranged from 4 to 16 Umg(-1) protein in the respective developmental stages. Substrate specificity was analysed using specific inhibitors (eserine sulphate, DPDA, BW284c51). The results showed that the observed cholinesterase activities in the whole embryo may be attributed mainly to acetylcholinesterase with a partial capability to use propionylthiocholine as a second substrate. The potential use of cholin- and carboxylesterase as biomarkers was investigated using the organophosphate paraoxon-methyl. A 40% inhibition of enzyme activities was reached by 0.4 microM paraoxon-methyl indicating the possible use of these enzymes as biomarkers of exposure.

The effects of environmental pollutants on complex fish behaviour: integrating behavioural and physiological indicators of toxicity

Environmental pollutants such as metals, pesticides, and other organics pose serious risks to many aquatic organisms. Accordingly, a great deal of previous research has characterized physiological mechanisms of toxicity in animals exposed to contaminants. In contrast, effects of contaminants on fish behaviour are less frequently studied. Because behaviour links physiological function with ecological processes, behavioural indicators of toxicity appear ideal for assessing the effects of aquatic pollutants on fish populations. Here we consider the many toxicants that disrupt complex fish behaviours, such as predator avoidance, reproductive, and social behaviours. Toxicant exposure often completely eliminates the performance of behaviours that are essential to fitness and survival in natural ecosystems, frequently after exposures of lesser magnitude than those causing significant mortality. Unfortunately, the behavioural toxicity of many xenobiotics is still unknown, warranting their future study. Physiological effects of toxicants in the literature include disruption of sensory, hormonal, neurological, and metabolic systems, which are likely to have profound implications for many fish behaviours. However, little toxicological research has sought to integrate the behavioural effects of toxicants with physiological processes. Those studies that take this multidisciplinary approach add important insight into possible mechanisms of behavioural alteration. The most commonly observed links with behavioural disruption include cholinesterase (ChE) inhibition, altered brain neurotransmitter levels, sensory deprivation, and impaired gonadal or thyroid hormone levels. Even less frequently studied are the implications of interrelated changes in behaviour and physiology caused by aquatic pollutants for fish populations. We conclude that future integrative, multidisciplinary research is clearly needed to increase the significance and usefulness of behavioural indicators for aquatic toxicology, and aim to highlight specific areas for consideration.

Gender differences in the effect of salinity on aldicarb uptake, elimination, and in vitro metabolism in Japanese medaka, Oryzias latipes

Toxicity studies have shown that salinity enhances the toxicity of aldicarb to female Japanese medaka. Although previous studies indicated that biotransformation may be important in these effects, other dispositional factors may play a role in this scenario. Male and female medaka were separately acclimated to three salinity regimens: 1.5, 12, and 20 parts per thousand (per thousand) for 2 weeks. The fish were then aqueously exposed to 96 h LC(20) of [(14)C]aldicarb for 24 h. [(14)C]aldicarb equivalents (aldicarb and its metabolites) were measured in whole-fish homogenates of half the fish. The other half of the population was transferred to clean water for 48 h. During this 48 h period, fish were removed and whole animal homogenates were measured radiometrically at 0, 2, 4, 8, 12, and 24 h time points. Salinity did not have an effect on the uptake of aldicarb in either male or female medaka. Elimination data showed that elimination of [(14)C]aldicarb equivalents was biphasic. Salinity did not have an effect on the elimination half life in either males or females. In vitro metabolism using gill and liver microsomes from fish acclimated to three salinity regimens showed that aldicarb sulfoxide production by male gill microsomes increased 6-fold by salinity compared to a 9-fold increase in female gills. In conclusion, the increased sensitivity of female medaka to salinity enhanced toxicity seems to be caused by a higher metabolic activation of aldicarb to the sulfoxide compared to the males. This study supports the hypothesis that the differential expression and regulation of FMOs is an important factor in determining the sensitivity of euryhaline fish to aldicarb, especially at high salinity regimens.

Influence of temperature and dissolved oxygen on the acute toxicity of profenofos to fathead minnows (Pimephales promelas)

The purpose of this study was to investigate the influence of temperature and dissolved oxygen levels on the acute toxicity of profenofos to fathead minnows (Pimephales promelas). Exposure conditions were as follows: normal temperature and normal dissolved oxygen (NTNO; 20 +/- 2 degrees C and 6.0-9.0 mg/L, respectively); normal temperature and low dissolved oxygen (NTLO; 20 +/- 2 degrees C and 1.7-2.6 mg/L, respectively); high temperature and normal dissolved oxygen (HTNO; 30 +/- 2 degrees C and 6.6-6.9 mg/L, respectively); high temperature and low dissolved oxygen (HTLO; 30 +/- 2 degrees C and 1.5-3.0 mg/L, respectively). Initial 96-h acute toxicity studies with profenofos were conducted at NTNO and HTLO exposure conditions. The 96-h LC50 at NTNO was 333 micrograms/L with 95% confidence limits ranging from 244 to 558 micrograms/L. However, the 96-h LC50 at HTLO was significantly lower at 21.5 micrograms/L with 95% confidence limits ranging from 17.4 to 28.8 micrograms/L. Acetylcholinesterase (AChE) activity was measured in the head and torso of surviving fish at 96-h. A weak dose-related decrease in AChE was observed at NTNO but no dose-response relationship was observed at HTLO exposure condition. Additional experiments were conducted using 50 micrograms/L profenofos at NTNO, NTLO, HTNO, and HTLO exposure conditions. Mortality, sublethal effects (erratic and hyperactive swimming), and AChE activity in the head and torso were measured at 2, 4, and 12-h following exposure to profenofos. No mortality or significant sublethal effects were observed in controls or profenofos-treated groups in NTNO and NTLO exposure conditions. However, significant mortality and sublethal effects were observed in profenofos-treated fish in HTNO at 12 h and at all time points in HTLO. Both high temperature and low dissolved oxygen, as well as combinations of high temperature and low dissolved oxygen significantly decreased AChE activity in control fish. Exposure to 50 micrograms/L profenofos in all exposure conditions further decreased AChE activity, but no apparent correlations between mortality and AChE activity were observed. These results suggest that the acute toxicity of profenofos to fathead minnows may be exacerbated during summer conditions in southern U.S. aquatic ecosystems.