Linking in situ bioassays and population dynamics of macroinvertebrates to assess agricultural contamination in streams of the Argentine pampa

Integrated biomarker responses in wild populations of the intertidal sea anemone Bunodosoma zamponii living under different anthropogenic pressures

Bunodosoma zamponii is the most abundant anemone in Mar del Plata (Buenos Aires, Argentina). Given that the presence of persistent organic pollutants (organochlorine pesticides and PCBs) and the organophosphate pesticide chlorpyrifos has recently been reported in this species, two wild populations living under different anthropogenic pressures were studied and compared regarding basic aspects of their ecology and physiological response to oxidative stress. A population from an impacted site (Las Delicias, LD) and another from a reference site (Punta Cantera, PC) were monitored seasonally (spring, summer, autumn, and winter), for one year. Anemones from PC were larger and more abundant than those from LD for most sampling periods. During winter, glutathione-S-transferase and catalase activities were higher in LD. Moreover, protein content and antioxidant defenses were higher in anemones from PC during winter as well. Taking into account their ecology (size and abundance) and biomarker responses, the population from PC was comparatively healthier. Furthermore, such differences are in agreement with recent studies indicating a higher concentration of pollutants in anemones from LD (specially during the winter sampling). In this sense, considering that B. zamponii can bioaccumulate the aforementioned pollutants, its resilience to their presence, and the fact that biomarker response differed between sites, this species can be regarded as a proper sentinel species of environmental pollution. Overall, this anemone seems to be a good bioindicator to be considered in future biomonitoring and ecotoxicological studies.

Ecological risk assessment of pesticides in sediments of Pampean streams, Argentina

After their application in agricultural areas, pesticides are dispersed throughout the environment, causing contamination problems. In Argentina, the main promoter of transgenic biotechnology in the region, the total consumption of agrochemicals has increased significantly in recent years. Most chemicals dumped near surface waters eventually end up in bottom sediments and can be toxic to the organisms that live there. However, published data on the mixing of pesticides in this compartment is still scarce. The objective of this work was to detect and quantify pesticide residues in the sediment of rural streams in the Pampas region and to carry out acute and chronic risk assessment in these aquatic ecosystems. The study area comprises the mountainous system of Tandilia, located in one of the most productive agricultural areas in the country. The concentration of atrazine, acetochlor, chlorpyrifos, cypermethrin, and 2,4-D in the sediment of four rural streams was determined in three different seasons, and the toxic units (TU) and the risk ratios (RQ) were calculated. All the compounds analyzed were detected in most of the sampling seasons and study sites, at concentrations higher than those established in the national and international quality guidelines for the protection of aquatic biota in surface waters and for human consumption. Chlorpyrifos, cypermethrin, and acetochlor were the main pesticides contributing to the TU and RQ values, representing a medium or high ecological risk in most of the sites. Therefore, the evaluation of these pesticides in the bottom sediments could be a decisive factor in assessing the risk to the aquatic environment.

Organochlorine pesticides and chlorpyrifos in the sea anemone Bunodosoma zamponii (Actiniaria: Actiniidae) from Argentina's southeastern coast

Temporal and spatial distribution of organochlorine pesticides (OCPs) and the organophosphate pesticide chlorpyrifos, one of the main insecticides used in Argentina, was evaluated in two populations of the sea anemone Bunodosoma zamponii living under different anthropological stressors: Las Delicias (LD) adjacent to a wastewater plant, and Punta Cantera (PC) a reference site. Pesticides were analyzed throughout the year in water, sediments and whole organisms. Chlorpyrifos represented 50% of the total pesticide found in water samples during winter. HCHs and drins were predominant in sediment samples, mainly in LD. Total pesticide concentration in anemones from LD was higher than those from PC during winter (mainly associated with HCHs, endosulfans, DDTs and chlorpyrifos levels), coincident with the main period of effluent discharge to the coast after pesticide applications and also the rainiest season. Dissimilarities among anemones populations could stem from a differential input of pesticides in each site and/or a contrasting physiological status of the populations.

Comparing production and life-history traits of a key amphipod species within and between estuaries under different levels of anthropogenic pressure

Inter-population variability may arise as a response to adverse natural and anthropogenic stressors. The dynamics of a key amphipod species (Echinogammarus marinus) was followed during ≈ 1-year at its southerly range (NW Portugal), in three estuaries with different levels of anthropogenic pressure (High - Ave estuary; Moderate - Mondego estuary; Low - Minho estuary). We hypothesised that E. marinus populations would present lower production and fitness, and higher intersexuality incidence with increasing anthropogenic pressure. According to a GAM model explaining ≈70% of the observed variability, E. marinus biomass depends on temperature, organic matter, Fucus area and time of the year. Significant differences were found between the gammarid biomass in Minho and Mondego estuaries and within sites from the same estuary. As expected, Ave estuary exhibited the lowest average annual production, abundance and fecundity rates. However, the highest average production was found in Mondego and not in Minho estuary, although the turnover ratio (P/B) of both estuaries was very similar. Besides the system's global ecological status, E. marinus also seems to respond to microhabitat conditions, which may explain the spatial heterogeneity observed in the amphipod production within the same estuary. Intersexuality prevalence was negligible in the three populations, which does not support the idea of a link between anthropogenic pressure and intersexuality in E. marinus. We argue that the dependence of E. marinus on Fucus sp. should be further investigated to fully understand the role of both fucoids and the gammarid in coastal foodwebs.

Pesticides Burden in Neotropical Rivers: Costa Rica as a Case Study

Neotropical ecosystems are highly biodiverse; however, the excessive use of pesticides has polluted freshwaters, with deleterious effects on aquatic biota. This study aims to analyze concentrations of active ingredients (a.i) of pesticides and the risks posed to freshwater Neotropical ecosystems. We compiled information from 1036 superficial water samples taken in Costa Rica between 2009 and 2019. We calculated the detection frequency for 85 a.i. and compared the concentrations with international regulations. The most frequently detected pesticides were diuron, ametryn, pyrimethanil, flutolanil, diazinon, azoxystrobin, buprofezin, and epoxiconazole, with presence in >20% of the samples. We observed 32 pesticides with concentrations that exceeded international regulations, and the ecological risk to aquatic biota (assessed using the multi-substance potentially affected fraction model (msPAF)) revealed that 5% and 13% of the samples from Costa Rica pose a high or moderate acute risk, especially to primary producers and arthropods. Other Neotropical countries are experiencing the same trend with high loads of pesticides and consequent high risk to aquatic ecosystems. This information is highly valuable for authorities dealing with prospective and retrospective risk assessments for regulatory decisions in tropical countries. At the same time, this study highlights the need for systematic pesticide residue monitoring of fresh waters in the Neotropical region.

Does the environmental condition affect the tolerance of the bivalve Anomalocardia flexuosa to different intensities and durations of marine heatwaves?

Populations of the clam Anomalocardia flexuosa, subjected to different pollution conditions, were experimentally exposed to marine heatwaves of actual and future intensities and varying durations. We measured physiological and biochemical biomarkers and survival rates of the species under simulated heatwave events of 7 and 11 days. We observed that both the response of A. flexuosa to heatwaves and its baseline values of biomarkers were distinct between populations, demonstrating that the previous exposure to contaminants negatively interferes with the thermal tolerance of this bivalve. The duration and intensities of heatwaves here tested represent a considerable challenge for the survival of coastal bivalves. Our results suggest that the predicted increase in the ocean's average temperature and the frequency and intensity of marine heatwaves, as well as urbanization and increasing occupation of coastal regions, are factors that synergistically make A. flexuosa increasingly vulnerable over the decades.

Ecotoxicological responses of a reef calcifier exposed to copper, acidification and warming: A multiple biomarker approach

Multiple global and local stressors threat coral reefs worldwide, and symbiont-bearing foraminifera are bioindicators of reef health. The aim of this study was to investigate single and combined effects of copper (Cu) and climate change related stressors (ocean acidification and warming) on a symbiont-bearing foraminifer by means of an integrated biomarker analysis. Using a mesocosm approach, Amphistegina gibbosa were exposed for 25 days to acidification, warming and/or Cu contamination on a full orthogonal design (two levels each factor). Cu was the main factor increasing bleaching and respiration rates. Warming was the main cause of mortality and reduced growth. Calcification related enzymes were inhibited in response to Cu exposure and, in general, the inhibition was stronger under climate change. Multiple biological endpoints responded to realistic exposure scenarios in different ways, but evidenced general stress posed by climate change combined with Cu. These biological responses drove the high values found for the 'stress index' IBR (Integrated Biomarker Response) - indicating general organismal health impairment under the multiple stressor scenario. Our results provide insights for coral reef management by detecting potential monitoring tools. The ecotoxicological responses indicated that Cu reduces the tolerance of foraminifera to climate change (acidification + warming). Once the endpoints analysed have a high ecological relevance, and that responses were evaluated on a classical reef bioindicator species, these results highlight the high risk of climate change and metal pollution co-exposure to coral reefs. Integrated responses allowed a better effects comprehension and are pointed as a promising tool to monitor pollution effects on a changing ocean.

Differential detoxifying responses to crude oil water-accommodated fraction in Hyallela curvispina individuals from unpolluted and contaminated sites

Sublethal effects of water-accommodated fraction (WAF) from crude oil of Neuquén basin, Northern Patagonia-Argentina, were examined on both antioxidant and detoxification system of Hyalella curvispina adults collected in Los Barreales (LB) lake and in an oil-polluted stream (DS). The effects of WAF exposure during 6, 24 and 48 h were evaluated in the glutathione content (GSH) and glutathione S-transferase (GST), catalase (CAT) and cytochrome P450 (CYP450) activities. Populations from DS and LB showed not only different basal GSH content and enzyme activities but also different behavior to WAF exposure. LB population exposed to WAF showed a significant increase in GSH content, CAT and CYP450 activities, compared to control group. DS population presented high basal levels in CAT and CYP activity compared with LB population, but their response to WAF exposure was minor. Amphipods from DS, chronically exposed to hydrocarbons, were adapted to their environment.

Joint Probabilistic Analysis of Risk for Aquatic Species and Exceedence Frequency for the Agricultural Use of Chlorpyrifos in the Pampean Region, Argentina

The Pampa Húmeda region in Argentina is characterized by soybean, wheat, and maize production, with intensive application of agrochemicals such as herbicides and insecticides. We used a joint probabilistic approach to analyze the probabilities for environmental chlorpyrifos concentrations measured in the Pampa Húmeda to exceed acute or chronic hazardous concentration for 5% of the species (HC5) values estimated from species sensitivity distributions for aquatic species. Chlorpyrifos concentrations in water ranged from 0.0005 to 10.8 µg/L, with a median of 0.013 µg/L. The HC5 limits were 0.0637 µg/L for acute and 0.0007 µg/L for chronic effects. The probabilities for chlorpyrifos environmental concentrations to exceed the HC5 values ranged from 35% (acute effects) to 96% (chronic effects). Water quality criteria (WQC) for the protection of aquatic life were also frequently exceeded (by 48-87%) for both acute and chronic effects. Together with published threshold limit values from mesocosm studies, these data suggest that macroinvertebrate communities can be severely affected by the reported environmental concentrations of chlorpyrifos. Indeed, changes in the macroinvertebrate assemblage in the Pampa Húmeda have been correlated with chlorpyrifos levels in sediments. Nevertheless, the actual impact needs to be ascertained by assessing the recovery rate of macroinvertebrate populations in this region. Considering the HC5 for chronic effects and the threshold limits for macroinvertebrate community level effects, we propose 0.7 ng/L as a new WQC to effectively protect aquatic life from long-term exposure to chlorpyrifos. Environ Toxicol Chem 2019;38:1748-1755. © 2019 SETAC.

Chemical characterization and toxicity of water-accommodated fraction of oil on the South American native species Hyalella curvispina

Chemical and toxicological crude oil analysis was performed on water-accommodated fraction of oil (WAF). This study characterized the chemical composition of WAF and its dissipation over a period of 192 h. Acute (96 h) and chronic (14 d) toxicity of WAF were evaluated on Hyalella curvispina from both reference (Los Barreales lake, LB) and hydrocarbon-contaminated (Durán stream, DS) sites. The total hydrocarbon (TPHs) concentration in WAF was 2.18 mg L^-1. The dissipation rates of hydrocarbons in WAF showed a first-order kinetics, with half-lives ranging between 65 h-200 h. Amphipods from LB showed acute and chronic LC50 values of 0.33 and 0.018 mg L^-1, respectively. Amphipods from DS exposed to pure WAF showed no mortality in either acute or chronic assays. Further biochemical and molecular research is required to determine the mechanisms underlying the resistance to WAF exposure on DS amphipods.

Aquatic macroinvertebrate assemblages are affected by insecticide applications on the Argentine Pampas

Agriculture intensification in Argentina has increased agrochemicals consumption in the last decades and might represent an environmental risk for adjacent water bodies. The objective of the present work was to assess the effect of land use on water quality and invertebrate assemblages in the Argentine Pampas streams. Eight streams were sampled on 4 occasions during the 2013/14 growing season. Three streams are located within a biosphere reserve, two drain basins with extensive livestock fields, and three run through intensively cultivated plots; one of them contained a 30m wide uncultivated grass-covered strip between the crop and the stream. Macroinvertebrates were sampled from emergent vegetation by means of a D-net with a 500µm pore size, and 30cm diameter. Higher nutrient concentrations were measured in the agricultural streams. Endosulfan was measured in sediments of the agricultural streams, concentrations being significantly lower in the stream with the buffer strip. Invertebrate assemblages in the cropped streams were significantly different from those in the livestock and reserve streams, those in the latter not being different from each other. Ampullaridae (Pomacea canaliculata) and Planorbidae (Biomophalaria peregrina) were the taxa best represented in the agricultural streams. Hyalellidae (Hyalella curvispina), Zygoptera and Planorbidae (B. peregrina) were the taxa best represented in the reserve and livestock streams. Present evidence suggests that the observed differences in the invertebrate composition in the agricultural streams were related with the impact of agrochemicals and that buffer strips represent a useful attenuation practice. Cattle breeding on natural pastures represented a land use with low impact on the invertebrate assemblages.

Structural and functional effects of a short-term pyrethroid pulse exposure on invertebrates in outdoor stream mesocosms

Agricultural land-use frequently results in short pulse exposures of insecticides such as pyrethroids in river systems, adversely affecting local invertebrate communities. In order to assess insecticide-induced effects, stream mesocosms are used within higher tier aquatic risk assessment. Regulatory acceptable concentrations (RACs) derived from those studies are often higher compared with tier 1 RACs. Hence, the present mesocosm study evaluates this aspect using a pulse exposure scenario typical for streams and the pyrethroid insecticide etofenprox. A 6-h pulse exposure with measured concentrations of 0.04, 0.3 and 5.3μgL^-1 etofenprox was used. We considered abundance, drift and emergence of invertebrates as structural endpoints and the in situ-measured feeding rates of the isopod Asellus aquaticus as functional endpoint. Most prominent effects were visible at 5.3μgL^-1 etofenprox which caused adverse effects of up to 100% at the individual and population level, as well as community structure alterations. Transient effects were observed for invertebrate drift (effect duration ≤24h) and for the invertebrate community (9 days after exposure) at 0.3μgL^-1 etofenprox. Furthermore, 0.04μgL^-1 etofenprox affected the abundance of the mayfly Cloeon simile (decrease by 66%) and the feeding rate of A. aquaticus (decrease by 44%). Thus, implications for the functional endpoint leaf litter breakdown in heterotrophic ecosystems may be expected. A hypothetical RAC derived from the present mesocosm study (0.004μgL^-1) is in line with the official tier 1 RAC (0.0044μgL^-1) and thus shows that the present mesocosm study did not result in a higher RAC.

Ecology of the non-native snail Sinotaia cf quadrata (Caenogastropoda: Viviparidae). A study in a lowland stream of South America with different water qualities

Sinotaia quadrata is a snail native from Asia recorded for the first time in South America in 2009 in central Argentina. In 2015, this species was also found in a lowland stream with different water qualities. Our aims were to contribute to the knowledge of its population ecology and to compare the individuals from the two locations anatomically. Snails were searched at 6 sites, where physicochemical and hydraulic parameters were measured. Biological samples were also taken at two sites (S3 and S4) to study the population traits of S. cf quadrata (density, size structure, fecundity and sex ratio) and to assess the water quality through macroinvertebrates' biological indices (richness, diversity and IBPamp). Physicochemical and biological parameters allowed us classifying sites as "moderately polluted" (S3) and "heavily polluted" (S4). At S4, the population showed a lower density, larger individuals, higher fecundity and a scarce representation of young snails. The differences observed in the radula and mantle border of snails from the two geographical regions might be attributed to environmental differences. We conclude that this species is tolerant to a wide range of environmental variables which, along with its high fecundity and morphological plasticity, could allow this species to colonize neighbor streams.

Species at Risk (SPEAR) index indicates effects of insecticides on stream invertebrate communities in soy production regions of the Argentine Pampas

We investigated relationships among insecticides and aquatic invertebrate communities in 22 streams of two soy production regions of the Argentine Pampas over three growing seasons. Chlorpyrifos, endosulfan, cypermethrin, and lambda-cyhalothrin were the insecticides most frequently detected in stream sediments. The Species at Risk (SPEAR) pesticide bioassessment index (SPEARpesticides) was adapted and applied to evaluate relationships between sediment insecticide toxic units (TUs) and invertebrate communities associated with both benthic habitats and emergent vegetation habitats. SPEARpesticides was the only response metric that was significantly correlated with total insecticide TU values for all three averaged data sets, consistently showing a trend of decreasing values with increasing TU values (r2=0.35 to 0.42, p-value=0.001 to 0.03). Although pyrethroids were the insecticides that contributed the highest TU values, toxicity calculated based on all insecticides was better at predicting changes in invertebrate communities than toxicity of pyrethroids alone. Crustaceans, particularly the amphipod Hyalella spp., which are relatively sensitive to pesticides, played a large role in the performance of SPEARpesticides, and the relative abundance of all crustaceans also showed a significant decreasing trend with increasing insecticide TUs for two of three data sets (r2=0.30 to 0.57, p-value=0.003 to 0.04) examined. For all data sets, total insecticide TU was the most important variable in explaining variance in the SPEARpesticides index. The present study was the first application of the SPEAR index in South America, and the first one to use it to evaluate effects of pesticides on invertebrate communities associated with aquatic vegetation. Although the SPEAR index was developed in Europe, it performed well in the Argentine Pampas with only minor modifications, and would likely improve in performance as more data are obtained on traits of South American taxa, such as pesticide sensitivity and generation time.

Multi-level biological responses in Ucides cordatus (Linnaeus, 1763) (Brachyura, Ucididae) as indicators of conservation status in mangrove areas from the western atlantic

There is a global lack of knowledge on tropical ecotoxicology, particularly in terms of mangrove areas. These areas often serve as nurseries or homes for several animal species, including Ucides cordatus (the uçá crab). This species is widely distributed, is part of the diet of human coastal communities, and is considered to be a sentinel species due to its sensitivity to toxic xenobiotics in natural environments. Sublethal damages to benthic populations reveal pre-pathological conditions, but discussions of the implications are scarce in the literature. In Brazil, the state of São Paulo offers an interesting scenario for ecotoxicology and population studies: it is easy to distinguish between mangroves that are well preserved and those which are significantly impacted by human activity. The objectives of this study were to provide the normal baseline values for the frequency of Micronucleated cells (MN‰) and for neutral red retention time (NRRT) in U. cordatus at pristine locations, as well to indicate the conservation status of different mangrove areas using a multi-level biological response approach in which these biomarkers and population indicators (condition factor and crab density) are applied in relation to environmental quality indicators (determined via information in the literature and solid waste volume). A mangrove area with no effects of impact (areas of reference or pristine areas) presented a mean value of MN‰<3 and NRRT>120min, values which were assumed as baseline values representing genetic and physiological normality. A significant correlation was found between NRRT and MN, with both showing similar and effective results for distinguishing between different mangrove areas according to conservation status. Furthermore, crab density was lower in more impacted mangrove areas, a finding which also reflects the effects of sublethal damage; this finding was not determined by condition factor measurements. Multi-level biological responses were able to reflect the conservation status of the mangrove areas studied using information on guideline values of MN‰, NRRT, and density of the uçá crab in order to categorize three levels of human impacts in mangrove areas: PNI (probable null impact); PLI (probable low impact); and PHI (probable high impact). Results confirm the success of U. cordatus species' multi-level biological responses in diagnosing threats to mangrove areas. Therefore, this species represents an effective tool in studies on mangrove conservation statuses in the Western Atlantic.

Land use effect on invertebrate assemblages in Pampasic streams (Buenos Aires, Argentina)

Agriculture and livestock may contribute to water quality degradation in adjacent waterbodies and produce changes in the resident invertebrate composition. The objective of the present study was to assess land use effects on the stream invertebrate assemblages in rural areas of the Argentine Pampa. The four sampling events were performed at six sites in four streams of the Pampa plain; two streams were sampled inside a biosphere reserve, and another one was surrounded by extensive livestock fields. The fourth stream was sampled at three sites; the upstream site was adjacent to agricultural plots, the following site was adjacent to an intensive livestock plot and the downstream site was adjacent to extensive breeding cattle plots. Higher pesticide concentrations were found at the site adjacent to agricultural plots and higher nutrient concentrations at the sites adjacent to agricultural and intensive breeding cattle plots. The invertebrate fauna were also different at these sites. Multivariate analysis showed a relationship between nutrient concentrations and taxonomic composition. Amphipoda (Hyalella curvispina) was the dominant group in the reserve and extensive breeding cattle sites, but was not present in the agricultural site. Also, Chironomidae were absent from the agricultural site while present at other sites. Gasteropoda (Biomphalaria peregrina), Zygoptera, and Hirudinea were dominant at the most impacted agricultural and intensive breeding cattle sites.

Examining impacts of current-use pesticides in Southern Ontario using in situ exposures of the amphipod Hyalella azteca

In situ exposures with Hyalella azteca were used to assess impacts of current-use pesticides in Southern Ontario, Canada. Exposures were conducted over 2 growing seasons within areas of high pesticide use: 1 site on Prudhomme Creek and 3 sites on Twenty Mile Creek. Three sites on Spencer Creek, an area of low pesticide use, were added in the second season. Surface water samples were collected every 2 wk to 3 wk and analyzed for a suite of pesticides. Hyalella were exposed in situ for 1 wk every 4 wk to 6 wk, and survival and acetylcholinesterase (AChE) activity were measured. Pesticides in surface waters reflected seasonal use patterns: lower concentrations in spring and fall and higher concentrations during summer months. Organophosphate insecticides (chlorpyrifos, azinphos methyl, diazinon) and acid herbicides (2,4-dichlorophenoxyacetic acid [2,4-D], mecoprop) were routinely detected in Prudhomme Creek, whereas neutral herbicides (atrazine, metolachlor) dominated the pesticide signature of Twenty Mile Creek. Spencer Creek contained fewer pesticides, which were measured at lower concentrations. In situ effects also followed seasonal patterns: higher survival and AChE activity in spring and fall, and lower survival and AChE activity during summer months. The highest toxicity was observed at Prudhomme Creek and was primarily associated with organophosphates. The present study demonstrated that current-use pesticides in Southern Ontario were linked to in situ effects and identified sites of concern requiring further investigation.

Insecticide concentrations in stream sediments of soy production regions of South America

Concentrations of 17 insecticides were measured in sediments collected from 53 streams in soy production regions of South America (Argentina in 2011-2014, Paraguay and Brazil in 2013) during peak application periods. Although environmental regulations are quite different in each country, commonly used insecticides were detected at high frequencies in all regions. Maximum concentrations (and detection frequencies) for each sampling event ranged from: 1.2-7.4 ng/g dw chlorpyrifos (56-100%); 0.9-8.3 ng/g dw cypermethrin (20-100%); 0.42-16.6 ng/g dw lambda-cyhalothrin (60-100%); and, 0.49-2.1 ng/g dw endosulfan (13-100%). Other pyrethroids were detected less frequently. Banned organochlorines were most frequently detected in Brazil. In all countries, cypermethrin and/or lambda-cyhalothrin toxic units (TUs), based on Hyalella azteca LC50 bioassays, were occasionally>0.5 (indicating likely acute toxicity), while TUs for other insecticides were <0.5. All samples with total insecticide TU>1 were collected from streams with riparian buffer width<20 m. A multiple regression analysis that included five landscape and habitat predictor variables for the Brazilian streams examined indicated that buffer width was the most important predictor variable in explaining total insecticide TU values. While Brazil and Paraguay require forested stream buffers, there were no such regulations in the Argentine pampas, where buffer widths were smaller. Multiple insecticides were found in almost all stream sediment samples in intensive soy production regions, with pyrethroids most often occurring at acutely toxic concentrations, and the greatest potential for insecticide toxicity occurring in streams with minimum buffer width<20 m.

Toxicity Persistence of Chlorpyrifos in Runoff from Experimental Soybean Plots to the Non-target Amphipod Hyalella curvispina: Effect of Crop Management

Toxicity persistence to the nontarget amphipod Hyalella curvispina in runoff events following chlorpyrifos applications to soy experimental plots was compared in conventional and no-till management. Two application scenarios were compared: an early-season application with the soil almost bare and a late-season application after the foliage had attained complete soil cover. H. curvispina was exposed to chlorpyrifos using two different test systems: a short-term (48 h) runoff water exposure and a long-term (10 days) soil exposure. Both commonly used crop management practices for soybean production resulted in runoff toxicity following pesticide applications and represent a toxicity risk for adjacent inland waters. Toxicity persistence was longer after the earlier than the late season application, likely because of higher volatilization and photodecomposition losses from the soy canopy than from the soil. For the early-season application, toxicity persisted longer in the no-till plots than in the conventional tillage plots. Suspended matter was higher in the conventional treatment. Chlorpyrifos sorption to suspended matter likely contributed to the shorter persistence. For the late-season application, toxicity persisted longer in the conventional treatment. The causes remain conjectural. The soil organic carbon content was higher in the no-till treatment. Sorption to organic matter might have contributed to the shorter chlorpyrifos toxicity persistence in no-till management. Late applications are more frequent and prevail longer throughout the soy growing season. Overall, the no-till management practice seems preferably because shorter toxicity persistence in runoff represents a lower environmental risk for the adjacent inland waters.

Pesticide effects on crabs: how environmental concentrations of endosulfan and chlorpyrifos affect embryos

The objectives of this work were to evaluate the effects of environmentally relevant chlorpyrifos and endosulfan, concentrations in the incubation period, effective hatching and survival of embryos and neonates of the freshwater burrowing crab, Zilchiopsis collastinensis (Decapoda, Trichodactylidae). Both pesticides were prepared from commercial and technical grade products. The exposure to about 100, 200, and 400 ng endosulfan L(-1), and 48, 240, and 1,200 ng chlorpyrifos L(-1) did not cause differences in the incubation period or in effective hatching but decreased survival of neonates, especially in the concentrations prepared from the technical grade product. Even if these concentrations are below the median lethal concentration (LC50) values for embryos, these caused a significant decrease in the survival of neonates, i.e. when crabs are outside the egg and not protected by chorion. The decrease in the neonate population caused by these concentrations, which could be found in the environment, might impact aquatic communities.

The impact of Eskoba, a glyphosate formulation, on the freshwater plankton community

This study analyzed the acute effects of a glyphosate-based herbicide (Eskoba) on the microalgae Chlorella vulgaris, the cladoceran Simocephalus vetulus, and the copepod Notodiaptomus conifer, and evaluated the recovery ability of the surviving micro-crustaceans. Survival, age of first reproduction, and fecundity were used as endpoints for S. vetulus, while survival and time to reach the adult stage were used as endpoints for N. conifer. The registered order of sensitivity was S. vetulus (48-hour effective concentration [EC50]: 21 mg/L) > C. vulgaris (72-hour EC50: 58.59 mg/ L) > N. conifer (48-hour EC50: 95 mg/L). Despite the growth of C. vulgaris stimulated after 24 hours of exposure to the commercial formulation of glyphosate Eskoba, it was inhibited after 48 hours by all the concentrations tested. In postexposure experiments, microcrustaceans reduced their life expectancy, S. vetulus decreased its fertility, and N. conifer inhibited its sexual maturity. In summary, it was demonstrated that these species lost their recovery ability.

Neurologic dysfunction and genotoxicity induced by low levels of chlorpyrifos

Chlorpyrifos (CPF) is an organophosphorus cholinesterase inhibitor widely used as an insecticide. Neuro and genotoxicity of this agent were evaluated following daily subcutaneous injections at 0.1, 1 and 10mg/kg or its vehicle to laboratory rats during one week, at the end of which somatosensory evoked potentials (SEP) and power spectrum of the electroencephalogram (EEGp) were recorded under urethane anesthesia. In another group of conscious animals, auditory startle reflex (ASR) was evaluated followed, after euthanasia, with measurements of plasma B-esterases, and genotoxicity with the alkaline comet assay (ACA) at the same CPF doses. The results indicated a CPF dose related inhibition of B-esterases. Enhanced inhibition of the ASR by a subthreshold pre-pulse was observed at all doses and ACA showed a significant higher DNA damage than vehicle controls in animals exposed to 10mg/kg CPF. A trend to higher frequencies of EEGp and an increase in amplitude of the first negative wave of the SEP were found at all doses. The first positive wave of the SEP decreased at the CPF dose of 10mg/kg. In summary, a shift to higher EEG frequencies and alterations of somatosensory and auditory input to the central nervous system were sensitive manifestations of CPF toxicity, associated with depression of B-esterases. The changes in electrical activity of the cerebral cortex and DNA damage observed at doses that do not elicit overt toxicity may be useful in the detection of CPF exposure before clinical signs appear.

Predator-prey imbalances due to a pesticide: density and applicability timing as determining factors for experimental assessments

Predator-prey relationships are determining factors in sustaining community structure but xenobiotics, including pesticides, have the potential to alter them, causing imbalances at the ecosystem level. Although invertebrate predation on zooplankton is of high importance in shallow lakes, there is still little information regarding disturbances on this trophic interaction. This work assessed the potential effects of a chlorpyrifos-based pesticide (CLP) on the interaction between prawns Macrobrachium borellii and cladocerans Ceriodaphnia dubia, taking into account prey densities, specific time of exposure and contamination level. The analysis was focused on the specific sensitivity of both species and, especially, on the predation rate of M. borellii on C. dubia. The latter was evaluated through different treatments that combined predator and/or prey exposure to the insecticide, before (lapse of 12 h) or during the interaction. Under low prey density, when prawns were previously exposed to the insecticide, their consumption rate was lower than that of controls. Conversely, when cladocerans or both species were previously exposed, the prawns' feeding rate was higher. Under high prey density, there were no substantial differences among treatments. Comparatively, cladocerans were significantly more consumed when the exposure of both species was performed before rather than during the interaction. From the results obtained, it can be assumed that the trophic interaction under study is sensitive to CLP and that individual density and specific time of exposure are important variables to be considered in similar studies in order to obtain realistic results.

Biochemical responses of ecological importance in males of the austral South America amphipod Hyalella curvispina Shoemaker, 1942 exposed to waterborne cadmium and copper

The use of physiological parameters as sensitive indicators of toxic stress from exposure to different pollutants is an important issue to be studied. Hyalella curvispina is a Neotropical amphipod often used in ecotoxicological evaluations. This work aimed to quantify biochemical responses of ecological importance in H. curvispina males under stress exposure to sublethal concentrations of waterborne copper (Cu) and cadmium (Cd); in order to obtain basic physiological data as indicators of early effect on this species, on track to its standardization. In order to evaluate the physiological, biochemical and energetic status of the exposed animals, the following endpoints were selected: content of glycogen, total proteins, total lipids, triglycerides, glycerol, arginine, arginine phosphate, levels of lipid peroxidation (TBARS), and Na(+)/K(+)ATPase, catalase (CAT) and superoxide dismutase (SOD) activities. Our results show that the concentrations of Cu (135 and 175 µg/L) and Cd (6.5 and 10.5 µg/L) tested altered most of the biochemical variables measured (glycogen, total proteins, total lipids, triglycerides, arginine phosphate, TBARS, and SOD and Na(+)/K(+)ATPase activities). In addition, neither the levels of glycerol and arginine nor CAT activity were affected by exposure to either metal. Energy metabolism was similarly affected both by exposure to Cu and exposure to Cd. The results obtained show the existence of an energy imbalance associated with oxidative damage, suggesting a comprehensive response. This work represents a first contribution of the evaluation of the effect of two heavy metals in some parameters of oxidative stress and energy metabolism of H. curvispina males. The results indicate these parameters can provide a sensitive criterion for the assessment of early ecotoxicological effects of Cu and Cd in laboratory assays, on a native species representative of the zoobenthic and epiphytic communities of South America.

Dynamics of organochlorine contaminants in surface water and in Myriophyllum aquaticum plants of the River Xanaes in central Argentina during the annual dry season

The dynamics of organochlorine pesticides (OCPs) and their major metabolites were studied in surface waters and plants of the River Xanaes (province of Córdoba, Argentina) during the annual dry season. The results of the 5-month monitoring study (April to August 2010) showed similar low contamination levels in nonagricultural mountain and agricultural areas in both water and plants. The concentrations of compounds detected in the surface water were <4.5 ng L(-1), whereas concentrations of these substances in Myriophyllum aquaticum plants were <5 μg kg(-1) (dry weight) with the exception of trans-permethrin (17.6 μg kg(-1), dry weight). Because no notable differences in the contamination level between samples from the mountain and the agricultural area were observed, it was assumed that OCPs may not play an important role in today's pesticide use in this area. Furthermore, the concentration-time trends for OCPs in the submerged plants showed a generally similar elimination behaviour independent of compound and sampling site, thus indicating an integral rather then a substance-specific process, such as partitioning between the plant and the ambient water. As known, rooted macrophytes can take up contaminants by way of roots, so sediments may be the principal source. To understand the dynamics of these compounds in the river area more deeply, thus further research should include study of the river sediment.

Effects of peak exposure scenarios on Gammarus fossarum using field relevant pesticide mixtures

The present study investigated sublethal effects of a field relevant pesticide mixture (one herbicide, three fungicides, five insecticides) on Gammarus fossarum by considering different peak exposure scenarios, which may be generated by the inherent properties of vegetated ditches. Additional experiments aimed at the identification of germane exposure pathways (food and water). Therefore, G. fossarum were exposed in independent experiments to three scenarios, which differed besides in the peak concentration of the pesticide mixture also in the mixture's composition and exposure duration (n=20 per treatment). The exposure duration of 12 or 120 min was followed by a seven-day post-exposure observation period. At a constant concentration-time product, a lower exposure duration in concert with a proportionally higher peak concentration caused a substantially elevated ecotoxicity compared to a treatment with a longer exposure duration at a lower peak concentration. Given the importance of the insecticide lambda-cyhalothrin for the mixture's ecotoxicity it may be concluded that the fast mode of action of pyrethroids mainly explains this observation. Moreover, field relevant concentrations of the pesticide mixture applied at an exposure duration of 120 min resulted in reduced gammarids' feeding rate, which may be indicative for shifts in the ecosystem function of leaf litter breakdown and hence the provision of energy for local and downstream communities. Finally, the present study indicated that both pathways of exposure, namely via food or water, reduce gammarids' feeding rate synergistically. This suggests that both exposure pathways should be considered for compounds exhibiting a high Kow (e.g. pyrethroids) during the risk assessment of single substances and mixtures.

Current-use pesticides in stream water and suspended particles following runoff: exposure, effects, and mitigation requirements

The European Union's directive for sustainable use of pesticides requires implementing risk mitigation measures at streams threatened by pesticide entries. The need for mitigation measures was investigated at 10 stream sites within an intensively used arable region in central Germany by characterizing pesticide exposure following edge-of-field runoff and effects on the aquatic macroinvertebrates. Moreover, the influence of riparian buffer strip width (as a mitigation measure) at the sampling sites was considered. Generally, invertebrate fauna was dominated by pesticide-tolerant species, suggesting a high pesticide exposure at almost all sites. This result is also reflected by the elevated levels of suspended particle contamination in terms of toxic units (logTUMax  > -2), corresponding to one-hundredth of the median lethal concentration (LC50) to Daphnia magna. At two sites that received high aqueous-phase entries of the pyrethroid lambda-cyhalothrin (logTUMax  > -0.6), the abundance and number of sensitive species in terms of the species at risk index decreased during the pesticide application period. In contrast, no acute significant negative effects on macroinvertebrates were observed at sites characterised by low water-phase toxicity (logTUMax  < -3.5). An influence of riparian buffer strip width on pesticide exposure was not observed, supposedly because of the presence of erosion rills and ephemeral ditches. In conclusion, results show that mitigation measures (such as the improvement of currently present riparian buffer strips) are needed in the study area.

Cost of reproduction. Changes in metabolism and endosulfan lethality caused by reproductive behavior in Hyalella curvispina (Crustacea: Amphipoda)

Biocides are periodically applied in agricultural activities, reaching aquatic systems and acting upon the biota. Amphipods are widely used in toxicity tests because of their sensitivity to a wide range of pollutants. In this work, we report the differential lethality of a widely used pesticide, endosulfan, on the amphipod Hyalella curvispina at two life stages and in three different adult groups, males and females separated by sex and both sexes grouped together. In addition, oxygen consumption of adult groups was determined as a way to estimate the role of behavioral activities and exposure to endosulfan in metabolism shifts. There were no differences between the LC(50) of juveniles and the adults when they were separated by sex (p>0.05). Nevertheless, the LC(50) of adults without sexual differentiation was significantly lower than the LC(50) of juveniles and adults separated by sex (p<0.05). The oxygen consumption rate was higher when adults were grouped without sexual differentiation in the control group. The exposure to low concentrations of endosulfan causes an increase in oxygen consumption in all the treatments. The sexual behavior increased the metabolism and the sensitivity to endosulfan. In future evaluations, adults grouped without sexual differentiation, which were the most sensitive group, should be included in order to mimic the environmental conditions. Using only juveniles or adults separated by sex in toxicity tests may inaccurately estimate the lethality of biocides, especially in species with constant reproductive activities.

Acute toxicity of cypermethrin to the non target organism Hyalella curvispina

The acute toxicity of cypermethrin to the amphipod Hyalella curvispina was evaluated by means of a toxicity test under laboratory conditions. Cypermethrin is one of the most widely used insecticides in Argentina. H. curvispina is a widely distributed and commonly abundant component of the invertebrate assemblages in shallow waters of southern South America. The experiments were repeated three times. The mean 48-h LC(50) value for H. curvispina was estimated at 0.066μg/l. H. curvispina represents a good model for exotoxicological risk assessment.

Toxicity persistence in runoff and soil from experimental soybean plots following insecticide applications

Persistence of toxicity in runoff water and soil was investigated in experimental soybean plots subjected to successive runoff events following pesticide application. Runoff events were produced by irrigation using a sprinkler system. The pesticides applied were cypermethrin and endosulfan, which are widely used in soy production in Argentina. Toxicity tests were performed on two abundant components of the regional fauna, the amphipod Hyalella curvispina and the fish Cnesterodon decemmaculatus. Runoffs from two pesticide applications were assayed at different stages of the growing season: an early application when the soil was almost bare and a late one close to harvest, when the ground was covered by vegetation and just before soy leaves fell. Toxicity to H. curvispina in runoff ceased almost one month after the early application of the two pesticides, while it persisted for over three months after the late application. Soil toxicity to H. curvispina and runoff toxicity to C. decemmaculatus followed the same pattern. Higher temperatures and solar radiation are likely to have enhanced insecticide degradation after the early application. Lower temperatures and solar radiation in combination with increased organic matter from litter probably contributed to the longer persistence of toxicity recorded after the late application, as compared with the early application. Cypermethrin caused no mortality to C. decemmaculatus after the early application, while endosulfan toxicity persisted for almost four months after the late one.

Toxicity persistence in runoff water and soil in experimental soybean plots following chlorpyrifos application

Toxicity persistence in runoff water and soil was studied in experimental soybean plots in successive runoff events produced by an irrigation system. Three chlorpyrifos applications throughout the growing period were assayed. Runoff and soil toxicity to the amphipod Hyalella curvispina and the fish Cnesterodon decemmaculatus was assessed. Toxicity persistence to H. curvispina was shorter in the early and midseason applications (23-28 and 21-69 days in runoff and soil, respectively) and longer in the late application (more than 140 days). The same trend was observed for C. decemmaculatus: 13 days for early and 56 for the late application.

Cadmium toxicity assessment in juveniles of the Austral South America amphipod Hyalella curvispina

Hyalella curvispina is representative of zoobenthic communities in Austral South America. It is taxonomically close to Hyalella azteca and abundant in fresh water bodies of the pampasic region of Argentina. It is usually used as test organism in ecotoxicological studies at a regional level, and there is a strong concern to increase the knowledge of both their biology and their sensitivity to different toxic agents. The aim of the present work was to assess the effects of cadmium on H. curvispina juveniles exposed to concentrations expected in the water bodies of the distribution area of the species. Survival, growth and cadmium body burden were evaluated in aqueous and solid matrices under fixed experimental conditions. Animals were exposed in ten-day static toxicity bioassays to 2.5, 5.25 and 11.25 μg Cd/L for the aqueous-phase bioassays, and to 0.85, 2.8 and 5.6 mg Cd/Kg dry sediment for the solid-phase bioassays. In water only assays, the animals exposed to 11.25 μg Cd/L showed a significant decrease in survival and growth. In the sediment bioassays, no effect was observed on survival, and weight was significantly reduced at the highest concentration. Cadmium uptake was concentration dependent for both assay matrices and one order of magnitude higher in the aqueous medium than in the solid matrix. Results indicate that juveniles of H. curvispina are sensitive to cadmium concentrations expected in their environment and thus confirm their importance as test organisms for ecotoxicity assessment in water bodies within the distribution area of the species.

Bioavailability, ecotoxicity, and geological characteristics of trace lead in sediments from two sites on Negro River, Uruguay, South America

Bioassays of two sites along the Rio Negro in Uruguay indicate ecotoxicity, which could be attributable to trace concentrations of lead in river sediments. Monthly samples at two sites at Baygorria and Bonete locations were analyzed for both particle size and lead. Lead was determined by atomic spectrometry in river water and sediment and particle size by sieving and sedimentation. Data showed that Baygorria's sediments have greater percentage of clay than Bonete's (20.4 and 5.8%, respectively). Lead was measurable in Baygorria's sediments, meanwhile in Bonete's, it was always below the detection limit. In water samples, lead was below detection limit at both sites. Bioassays using sub-lethal growth and survival test with Hyalella curvispina amphipod, screening with bioluminescent bacteria Photobacterium leiognathi, and acute toxicity bioassay with Pimephales promelas fish indicated toxicity at Baygorria, with much less effect at Bonete. Even though no lethal effects could be demonstrated, higher sub-lethal toxicity was found in samples from Baygorria site, showing a possible concentration of the contaminant in the clay fraction.

Microcrustaceans escape behavior as an early bioindicator of copper, chromium and endosulfan toxicity

The purpose of this work was to experimentally analyze the impact of copper, chromium and a commercial pesticide with endosulfan on the escape behavior of two copepods (Notodiaptomus conifer, Argyrodiaptomus falcifer) and three cladocerans (Daphnia magna, Pseudosida variabilis and Ceriodaphnia dubia). The experimental assays were carried out using a novel hydraulic devise designed to mimic three-speed predator capture behavior. Two concentrations, one "high" and one "low", were employed and the exposure time was 15 (±5) minutes. With two exceptions, the species exposed to heavy metals manifested higher ability to escape than controls. Both concentrations of the pesticide reduced the escape ability of cladocerans but copepods responded, in general, in a similar manner as for heavy metals. The immediate apparent advantage of low and early toxic effects is discussed and the high sensitivity of the escape behavior suggests that it could be a complementary endpoint to be used in future ecotoxicological tests.

Exposure to sublethal chromium and endosulfan alter the diel vertical migration (DVM) in freshwater zooplankton crustaceans

Among zooplankton behaviors, diel migrations constitute one of the most effective predator avoidance strategy and confer metabolic and demographic advantages. We aim to examine whether sublethal concentrations of two widespread pollutants (a pesticide with endosulfan and chromium as potassium dichromate) alter the depth selection, vertical migration and grouping of five freshwater species: Argyrodiaptomus falcifer, Notodiaptomus conifer, Pseudosida variabilis, Ceriodaphnia dubia and Daphnia magna. In a series of experimental assays, performed with 150 cm length transparent tubes, we analyzed the ascents and descents movements through periods of 24 h. Among controls, the copepods showed a tendency to remain closest to the surface, however, N. conifer registered a downward movement of 18.14 cm between 06:00 and 12:00. The cladoceran P. variabilis occupied the deeper position (85 cm), C. dubia showed a tendency to hike to the surface at 06:00 (57.7 cm) descending to lower levels at 18:00. D. magna showed a constant movement of ascent between 00:00 and 18:00, making an average travel of 29.4 cm. When subjected to pollutants, these behaviors were altered. It is hypothesized that a reduction in swimming activity and disorientation would be the main cause of such alterations. The high sensitivity of this endpoint sugests it to be adecuate as a complement in future standard toxicity tests.

Insecticide toxicity to Hyalella curvispina in runoff and stream water within a soybean farm (Buenos Aires, Argentina)

Toxicity to the locally dominant amphipod Hyalella curvispina was assessed in a first-order stream running through a cultivated farm. Cypermethrin, chlorpyrifos, endosulfan and glyphosate were sprayed throughout the studied period. Toxicity was assayed under controlled laboratory conditions with runoff and stream water samples taken from the field under steady state and flood conditions. Ephemeral toxicity pulses were observed as a consequence of farm pesticide applications. After pesticide application, runoff water showed 100% mortality to H. curvispina for 1 month, but no mortality thereafter. Toxicity persistence was shortest in stream water, intermediate in stream sediments and longest in soil samples. Runoff had a more important toxicity effect than the exposure to direct aerial fumigation. The regional environmental features determining fast toxicity dissipation are discussed.

Effect of aquatic vegetation on the persistence of cypermethrin toxicity in water

Soybean production in Argentina comprises 15 million ha. Cypermethrin is the main insecticide applied amounting 150 g of active ingredient per hectare, thus representing roughly 2.3 thousand tons yearly released to the environment. Toxicity pulses have been observed in small streams draining agricultural basins, most of them sustaining macrophyte growth. Cypermethrin concentrations and its toxicity to the amphipod Hyalella curvispina was compared following an addition to laboratory mesocosms with and without a vegetation cover of the floating macrophyte Lemna sp. Both concentrations and toxicity decreased faster in the treatments covered with Lemna. Fast adsorption of the hydrophobic pesticide to the roots and fronds of Lemna was suggested.

Numerical variations and spontaneous malformations in the early embryos of the Korean salamander, Hynobius leechii, in the farmlands of Korea

Embryo sacs of the Korean salamander, Hynobius leechii, were collected from nine farmlands in Gyeongsangnam-Do, Korea, in early spring of 2002 and 2004. The variations in the number of embryos within each embryo sac and the mortality and abnormality rates among the embryos were investigated. We also analyzed the patterns of spontaneous embryonic malformations and the residual chemicals in the soil of the habitats using multiple-residue GC/MS. A total of 79,195 embryos were obtained from 1933 embryo sacs. There were regional variations in the length of individual embryo sacs and the number of embryos in each. The longest embryo sac averaged by region measured 20.67 cm ± 3.51 and was obtained from 2-Banseong in 2002. Of the embryos collected, 13.71% either died or stopped developing, and 3.54% of the hatched embryos developed abnormally; the latter were classified according to the patterns of malformation. External gill dysplasia was the most frequent malformation, and caudal dysplasia, abdominal blisters, and dysplasia of the fin were also observed frequently. Histopathological analysis showed neural tube abnormalities, acrania, curved notochords, thyroid teratoma, and various other kinds of endodermal developmental abnormalities. In the analysis of the residual pesticides in the soil, carbofuran, endosulfan-sulfate, and endosulfan-β were detected in the regions with high mortality and malformation rates. These results indicate that various agricultural chemicals and other unknown factors may cause the aforementioned forms of spontaneous malformations in the embryos of Hynobius leechii.

Environmental impact of insecticides applied on biotech soybean crops in relation to the distance from aquatic ecosystems

Aquatic environments located in areas cultivated with biotech soybean were studied. Water and sediment samples were analyzed for insecticides, acute toxicity, genotoxicity, detoxification biomarkers, and fish diversity. Samples were taken in the core area of soybean cultivation in Argentina; all measures were related to the distance between the crops and the streams sampled. Endosulfan (alpha + beta) concentrations as high as 553.33 microg/kg were found in sediments from environments located at 0.15 m from treated fields. Ethoxyresorufin-O-deethylase (EROD) activity and cytochrome P4501A1 (CYP1A1) gene expression in fish showed the highest correlation with the environmental concentration of endosulfan. These biomarkers and mortality of amphipods significantly correlated with the concentration of endosulfan in water and sediment, which correlates inversely with the distance between the crop and streams. The differences with respective controls disappear at distances greater than 5 m. The fish diversity was significantly lower from distances between the margin of the stream and soybean crops, not exceeding 2 m.

Toxicity persistence following an experimental cypermethrin and chlorpyrifos application in Pampasic surface waters (Buenos Aires, Argentina)

The Pampa plain is intensively cultivated, the genetically modified glyphosate-resistant soybean being the main culture. A small first-order stream draining a cultured farm was studied. During the dry 2007 spring, the channel became a wetland with remnant intercalated shallow pools. Toxicity persistence of cypermethrin and chlorpyrifos to the amphipod Hyallela curvispina was assessed following a simulated plane application in the recently formed pools. In situ exposures and laboratory toxicity tests were performed. An ephemeral toxicity pulse lasting 4 h after the application and mortality cessation following that was observed.

Survival and growth of Palaemonetes argentinus (Decapoda; Caridea) exposed to insecticides with chlorpyrifos and endosulfan as active element

Pesticides with chlorpyrifos and endosulfan as active element are used for pest control on agricultural lands and are high-risk inputs in aquatic systems. The acute toxicity of these insecticides in the freshwater prawn Palaemonetes argentinus was evaluated. The results were used to determine the lowest observed-effect and no observed-effect concentrations. Individual growth of prawns in relation to chlorpyrifos and endosulfan exposure was analyzed. LC(50) values to chlorpyrifos and endosulfan exposure were 2.98 microg L(-1) and 14.10 at 24 hours and 0.49 microg L(-1) and 6.28 microg L(-1) at 96 hours of exposure, respectively. The size increment of prawns was the same in all treatments; cephalothorax length increased linearly per molt. The intermolt period was influenced by the toxic effect of pesticides during rearing time, and this decreased with the molt cycles compared with the normal growth pattern. The results suggest that juveniles of P. argentinus are sensitive to chlorpyrifos and endosulfan pollution.

Impact of cypermethrin on stream fish populations under field-use in biotech-soybean production

The impact of biotech-soybean technology on freshwater ecosystems is being evaluated in the Rolling Pampas region, Argentina. The effect of cypermethrin, the main soybean insecticide, on low-order temperate-stream fish populations was investigated for two consecutive crop cycles under field-use conditions in biotech-soybean production. Cypermethrin was unable to induce mortality or behavioral effects on any of the fish species resident in a first-order stream across a crop field (pulsed acute exposure scenario) sprayed according to conventional practices. No spatially or temporally dependent effects were observed on population parameters (size-class structure, abundance, survival, sex and immature/mature ratio, condition factor) of resident or caged Cnesterodon decemmaculatus after spraying or rainfall events, not even one year after, at the beginning of the next crop cycle. Although cypermethrin was "very highly toxic" to C. decemmaculatus in laboratory water (96h-LC(50)=0.43microg/l), its toxicity was reduced in filtered (78%) and unfiltered (92%) stream water. Changes in LC(50) values were mainly correlated with the OC content of each water fraction (r(2)=0.99; p<0.01; n=9), showing that both DOC and TOC contributed proportionally to toxicity reduction. Protective effects of stream water (12-fold reduction LC(50) values) explained the lack of effects on fish populations in the field, despite cypermethrin water concentrations after spraying reached values comparable with the 96h-LC(50). Therefore, cypermethrin under field-use conditions in transgenic-soybean production represents a low risk of acute exposure for fish populations inhabiting low-order temperate-streams rich in TOC. The relationship between LC(50) and TOC could be a convenient way to improve risk estimation based on laboratory toxicity testing.

In situ-based effects measures: determining the ecological relevance of measured responses

The aim of this review is to examine how the choice of test species and study design employed in the use of in situ approaches in ecological risk assessment can maximize the ecological relevance of data. We provide a framework to define and assess ecological relevance that permits study designs to remain focused on the ecological question being addressed. This framework makes explicit the linkages between effects at lower levels of biological organization and higher-order ecological effects at the population, community, and ecosystem levels. The usefulness of this framework is illustrated by reference to specific examples from aquatic ecotoxicology. The use of models as both interpretive and predictive tools is discussed, with suggestions of appropriate methods for different protection goals.

Assessment of insecticide contamination in runoff and stream water of small agricultural streams in the main soybean area of Argentina

The first- and second-order streams, Brown and Horqueta, respectively, which are located in the main area of soybean production in Argentina were examined for insecticide contamination caused by runoff from nearby soybean fields. The insecticides most widely used in Argentina (chlorpyrifos, cypermethrin and endosulfan) were detected in sediments, suspended particles and water. Highest concentrations in suspended particles were 318 microg/kg for endosulfan in the stream Horqueta, while 226 microg/kg chlorpyrifos and 13.2 microg/kg cypermethrin were measured in the stream Brown. In the Horqueta stream 150 and 53 microg/kg chlorpyrifos and cypermethrin were detected in runoff sediments, respectively. Whereas cypermethrin concentrations in the suspended particles were relatively low, levels in the floodwater of Brown reached 0.7 microg/l. The highest chlorpyrifos concentration in floodwater was 0.45 microg/l in Brown. However, endosulfan was not detected in the water phase. In runoff water the highest concentrations measured were 0.3 microg/l for chlorpyrifos in Horqueta and 0.49 microg/l for cypermethrin in the Brown stream. On five sampling dates during the pesticide application period in Brown stream (2002/2003) the concentration of chlorpyrifos and cypermethrin in runoff and/or floodwater exceeded the water quality criteria for freshwater mentioned in this study. In three cases this insecticide concentration was measured in stream water, indicating an acute risk to aquatic life. The acute toxicity-exposure-ratio (TER) for chlorpyrifos and cypermethrin also shows an acute risk for aquatic invertebrates in the Brown stream. In the Horqueta chlorpyrifos concentrations in the runoff exceeded the safety levels three times during the application period (2001/2002), potentially endangering the aquatic fauna. Effects on aquatic macroinvertebrates after insecticide contamination were reported in earlier studies in Horqueta stream.