Effects of azinphos-methyl on the reproductive success of the bluegill sunfish, Lepomis macrochirus, in littoral enclosures

Biomarker responses and morphological effects in juvenile tilapia Oreochromis mossambicus following sequential exposure to the organophosphate azinphos-methyl

Pesticides are contaminants of aquatic environments. Such ecosystems in the Western Cape, South Africa are at risk as most organophosphates are highly toxic to fish and other aquatic organisms. The objective of this experimental study was firstly to determine the acute toxicity of azinphos-methyl (AZP) to juvenile fish (Oreochromis mossambicus) and, secondly, to investigate the effects of repeated exposure of fish to an array of sublethal concentrations on morphological parameters such as growth, condition factor and organ-somatic indices. Food consumption and feeding response time were investigated as ecologically relevant behavioral endpoints which could affect growth, reproduction and survival and subsequently causes impacts at the population and/or community level. Finally, acetylcholinesterase (AChE) was used as biomarker to investigate effects at sub-organismal level following sequential exposure to AZP. The aim was to determine how sequential spraying procedures, using different exposure concentrations and intervals, affected fish as reflected by their responses at different organizational levels. A dose-dependent effect on feeding impairment was observed in the feeding response experiment. The correlation found between growth impairment, feeding activity and AChE inhibition therefore indicates that frequency of exposure can play an important role regarding the severity of impacts to non-target organisms. This study provides evidence that AZP has harmful effects on non-target aquatic organisms, such as fish which can be manifested in the early developmental stages. Sequential exposures showed that dosage and frequency of spraying and spraying interval could exacerbate harmful effects. AChE inhibition and organosomatic indices can be used effectively to measure effects.

Interspecific competition delays recovery of Daphnia spp. populations from pesticide stress

Xenobiotics alter the balance of competition between species and induce shifts in community composition. However, little is known about how these alterations affect the recovery of sensitive taxa. We exposed zooplankton communities to esfenvalerate (0.03, 0.3, and 3 μg/L) in outdoor microcosms and investigated the long-term effects on populations of Daphnia spp. To cover a broad and realistic range of environmental conditions, we established 96 microcosms with different treatments of shading and periodic harvesting. Populations of Daphnia spp. decreased in abundance for more than 8 weeks after contamination at 0.3 and 3 μg/L esfenvalerate. The period required for recovery at 0.3 and 3 μg/L was more than eight and three times longer, respectively, than the recovery period that was predicted on the basis of the life cycle of Daphnia spp. without considering the environmental context. We found that the recovery of sensitive Daphnia spp. populations depended on the initial pesticide survival and the related increase of less sensitive, competing taxa. We assert that this increase in the abundance of competing species, as well as sub-lethal effects of esfenvalerate, caused the unexpectedly prolonged effects of esfenvalerate on populations of Daphnia spp. We conclude that assessing biotic interactions is essential to understand and hence predict the effects and recovery from toxicant stress in communities.

Validation of an ecosystem modelling approach as a tool for ecological effect assessments

In ecotoxicology, derivation of a "safe" environmental concentration is usually achieved by the use of extrapolation factors or by statistical extrapolation from a set of single species toxicity data. These approaches ignore ecological interactions between species in the field. An ecology-based alternative to this pragmatic approach can be ecosystem modelling, which can account for ecological interactions. However, it is largely unexplored how well the predictions of these models quantitatively agree with large-scale experimental studies. Therefore, we evaluated the capacity of a flexible ecosystem model to predict population and ecosystem-level no observed effect concentrations (NOECs) of 7 organic toxicants. These NOECs were compared with population and ecosystem-NOECs observed in 11 micro- and mesocosm studies. For each of the latter studies, the model was customized to account for the specific ecological interactions within these systems and combined with appropriate single-species toxicity data from literature. Population-NOEC predictions were accurate, or at least protective, for 60, and 85% of all considered model populations, respectively. For all 11 studies, a protective ecosystem-NOEC could be derived, being accurate in 7 cases, and conservative in 4 cases. In general, it can be stated that this type of models can serve as an ecology-based alternative to current extrapolation techniques in EEAs and water quality standard setting.

Threshold levels for effects of insecticides in freshwater ecosystems: a review

A literature review of freshwater (model) ecosystem studies with neurotoxic insecticides was performed to assess ecological threshold levels, to compare these levels with the first tier approach within European Union (EU) administration procedures, and to evaluate the ecological consequences of exceeding these thresholds. Studies published between 1980 and 2001 were reviewed. Most studies covered organophosphates and synthetic pyrethroids in lentic waters. The most sensitive taxa were representatives of crustaceans, insects and fish. Based on toxic units, threshold values were equivalent for compounds with a similar mode of action. This also accounted for the nature and magnitude of direct effects at higher concentrations. Although laboratory single species toxicity tests may not allow predictions on precise ecological effects, some generalisations on effects and recovery can be made with respect to acute standard laboratory EC50 data. The NOEC(ecosystem) usually is a factor of 10 or more higher than first tier acceptable concentrations, particularly in the case of single applications and acetylcholinesterase inhibitors. Acceptable concentrations, as set by the EU first tier approach, appear to be protective. Recovery of sensitive endpoints usually occurs within 2 months of the (last) application when peak concentrations remain lower than (0.1-1) x EC50 of the most sensitive standard test species. The consistency of response patterns found in model ecosystem studies can be useful when estimating the ecological risks of pesticides. The use of an effect classification system was also helpful in evaluating effects.

Fate and effects of azinphos-methyl in a flow through wetland in South Africa

Our knowledge about the effectiveness of constructed wetlands in retaining agricultural nonpoint-source pesticide pollution is limited. A 0.44-ha vegetated wetland built along a tributary of the Lourens River, Western Cape, South Africa, was studied to ascertain the retention, fate, and effects of spray drift-borne azinphos-methyl (AZP). Composite water samples taken at the inlet and outlet during five spray drift trials in summer 2000 and 2001 revealed an overall reduction of AZP levels by 90 +/- 1% and a retention of AZP mass by 61 +/- 5%. Samples were collected at the inlet outlet, and four platforms within the wetland to determine the fate and effect of AZP in the wetland after direct spray drift deposition in the tributary 200 m upstream of the inlet. Peak concentrations of AZP decreased, and the duration of exposure increased from inlet (0.73 microg/L; 9 h) via platforms 1 and 4 to outlet (0.08 microg/L; 16 h). AZP sorbed to plants or plant surfaces, leading to a peak concentration of 6.8 microg/kg dw. The living plant biomass accounted for 10.5% of the AZP mass initially retained in the wetland, indicating processes such as volatilization, photolysis, hydrolysis, or metabolic degradation as being very important AZP was not detected in sediments. Water samples taken along two 10-m transects situated perpendicular to the shore indicated a homogeneous horizontal distribution of the pesticide: 0.23 +/- 0.02 and 0.14 +/- 0.04 microg/L (n = 5), respectively. Both Copepoda (p = 0.019) and Cladocere (p = 0.027) decreased significantly 6 h postdeposition and remained at reduced densities for at least 7 d. In parallel, the chlorophyll a concentration showed an increase, although not significant, within 6 h of spray deposition. The study highlights the potential of constructed wetlands as a risk-mitigation strategy for spray drift-related pesticide pollution.

Rainfall-induced sediment and pesticide input from orchards into the Lourens River, Western Cape, South Africa: importance of a single event

Rainfall-induced runoff transported sediments and pesticides into the Lourens River and its tributaries during a 28.8-mm rainstorm in mid-December 1998. Average 1-h peak levels of current-use insecticides applied to adjacent orchard plots were 1.5 micrograms l-1 azinphos-methyl, 0.2 microgram l-1 chlorpyrifos and 2.9 micrograms l-1 total endosulfan (alpha, beta, S) in the river itself. Respective average 1-h pesticide levels associated with suspended particles were 1247, 924 and 12,082 micrograms kg-1, along with 980 micrograms kg-1 of prothiofos. Total suspended solids increased during runoff from 32 to 520 mg l-1. The contaminated edge-of-field runoff entered the river via the tributaries directly bordering the orchard-growing areas. Increased concentrations of azinphos-methyl and prothiofos associated with suspended sediments were demonstrated to persist for about 3.5 months without any further input in one of the tributaries. This illustrates that the short-term exposure has the potential to result in long-term contamination of surface waters. In terms of chemical load during the 1-h peak discharge period, the single rainfall event caused a loss of 173 g h-1 azinphosmethyl, 55 g h-1 chlorpyrifos, 740 g h-1 total endosulfan (alpha, beta, S) and 41 g h-1 prothiofos. Levels of contamination were extremely high; they exceed the national water quality standards and those established by the US EPA. A comparison with standard toxicity data and 24-h LC50 s for the local amphipod species Paramelita nigroculus, obtained during this study, indicates that the concentrations found in the river may result in acute toxic effects on aquatic invertebrates and fishes. A probability analysis of 10-y rainfall data revealed that the frequency of a similar storm event occurring within the main spraying season is 1.7 y-1.

Persistence and distribution of azinphos-methyl following application to littoral enclosure mesocosms

The organophosphorus insecticide azinphos-methyl was applied once to the surface of 12 of 18 littoral enclosure mesocosms (5x10 m) constructed in a 2-ha pond near Duluth, Minnesota. Water, sediment, macrophytes, and adult fathead minnows were analyzed for residue to determine the persistence, distribution, and mass balance of azinphos-methyl. Nominal treatment concentrations were 0, 0.2, 1, 4, and 20 microg/liter active ingredient. The maximum residue concentration in the water was measured 1h after treatment. The half-life in the water column ranged from 1.2 to 2 days and 95% of the residue dissipated in 5.4 to 10.2 days. Measurable residues were found in the sediment, macrophytes, and fish. Maximum residues in these media were measured at 4, 1, and 0.12 days. respectively. The water and sediment were the most important sorptive compartments for azinphos-methyl residue. The macrophytes and fish were of minor importance, containing only trace amounts of the mass applied.

Mesocosms in ecotoxicology (1): Outdoor aquatic systems

Mesocosms have been used in aquatic ecotoxicology for approximately 20 years and were sometimes claimed to be essential tools, especially for regulatory purposes. The term aquatic mesocosm currently describes indoor and outdoor artificial streams or experimental ponds and enclosures. The use of mesocosms refines the classical methods of ecotoxicological risk assessment because mesocosms provide conditions for a better understanding of environmentally relevant effects of chemicals. They make it possible to assess effects of contaminants by looking at the parts (individuals, populations, communities) and the whole (ecosystems) simultaneously. Ecotoxicological investigations in mesocosms will not entirely replace the use of laboratory animals. However, they allow tests to be performed on species that are not of major societal concern, but which play key roles in the structure and function of ecosystems. In this respect, mesocosms allow nondestructive measurements of integrated endpoints. They also appear as potent tools to predict changes at the highest levels of organization (population, community, and ecosystem) from measurements of individual endpoints. However, after a period of extensive use, regulatory studies using large-scale mesocosms were more or less abandoned at the beginning of the 1990s, mainly because their cost-effectiveness was questionable. This review covers key features of outdoor aquatic mesocosms that can be critical for their use in environmental risk assessment of chemicals and emphasizes the optimization of their use for such purpose. The originality of mesocosms is mainly based on the combination of ecological realism, achieved by introduction of the basic components of natural ecosystems, and facilitated access to a number of physicochemical, biological, and toxicological parameters that can be controlled to some extent. This characteristic determines various features of the systems such as the minimal size required, initial physicochemical and biological composition, or choice of model species for ecotoxicological investigations. Ecological maturity of mesocosms affects the degree of variability of both physicochemical and biological parameters used to investigate the impact of contaminants. Adequate time is required to establish a number of interacting functional groups. The choice of appropriate time scales must be considered in the selection of both study duration and sampling frequency. Whatever the system used, duration of experiments should be sufficient to identify both direct and indirect effects on populations and communities. The choice of the experimental design should be based on the objectives of the study rather than on theoretical considerations. In addition to classical parametric statistical methods, nonparametric approaches and multivariate analysis may significantly improve data processing. Realism, representativity, and replicability of mesocosms are critical for evaluating their usefulness in both risk and impact assessment procedures. Each natural ecosystem is unique because its structure and function mainly depend on local factors. Therefore, there is a conceptual opposition between realism and replicability when applied to mesocosms. Considering the objectives of most mesocosm studies, replicability should be preferred to realism. Replicability may be achieved, in part, by a relative simplification of the systems. Reconstituted systems do not need to exactly simulate natural conditions at all levels, but key features at both structural and functional levels should be preserved as they ensure ecological representativity. Reliability of information on ecotoxicological effects of chemicals tested in aquatic mesocosms closely depends on the representativity of biological processes or structures that are likely to be affected. Extrapolation from small experimental systems to the real world seems generally more problematic than the use of larger systems in which more complex interacti

Development of monoclonal ELISAs for azinphos-methyl. 1. Hapten synthesis and antibody production

The development of monoclonal antibody-based enzyme-linked immunosorbent assays for azinphos-methyl is described. A panel of haptens was synthesized for immunoconjugate preparation, and a series of haptens for heterologous, coating or tracer, conjugates was also prepared. Hapten synthesis was based on a strategy in which only a fragment of the whole target molecule was present (fragmentary haptens). From immunized mice, a set of monoclonal antibodies was obtained and ELISA sensitivities were assayed in different formats. Affinities estimated as I(50) values in the low nanomolar range for azinphos-methyl and phosmet were observed for several monoclonal antibodies in the conjugate-coated format and in the antibody-coated format under nonoptimized assay conditions.

Effects of esfenvalerate on the reproductive success of the bluegill sunfish, Lepomis macrochirus in littoral enclosures

Adult bluegills were exposed to the synthetic pyrethroid esfenvalerate, during a reproduction study conducted in six littoral enclosures located in a 2-ha pond near Duluth, Minnesota. Bluegill reproductive success was determined after two applications of esfenvalerate at nominal concentrations of 0.0, 0.01, 0.08, 0.20, 1. 0, and 5.0 microg/L. Responses measured were adult behavior and spawning, embryo hatchability, larval survival until swim-up, young-of-the-year (Y-O-Y) growth, and total biomass. All adult bluegills died within one day following the first application at 5.0 microg/L. Successful spawning and resulting hatching of offspring were observed at all esfenvalerate concentrations except 5.0 microg/L. Following exposure at 1.0 microg/L, spawning was delayed for 15 days and few or no larvae survived. Bluegill Y-O-Y growth was reduced by 62, 57, and 86% in the 0.08, 0.20, and 1.0 microg/L esfenvalerate treated enclosures. Delayed adult spawning and reduced Y-O-Y growth may result in poor Y-O-Y overwinter survival which would result in a diminished or extirpated year class.