Aquatic community structure in Mediterranean edge-of-field waterbodies as explained by environmental factors and the presence of pesticide mixtures.

Studies addressing the predicted effects of pesticides in combination with abiotic and biotic factors on aquatic biota in ditches associated with typical Mediterranean agroecosystems are scarce. The current study aimed to evaluate the predicted effects of pesticides along with environmental factors and biota interactions on macroinvertebrate, zooplankton and phytoplankton community compositions in ditches adjacent to Portuguese maize and tomato crop areas. Data was analysed with the variance partitioning procedure based on redundancy analysis (RDA). The total variance in biological community composition was divided into the variance explained by the multi-substance potentially affected fraction [(msPAF) arthropods and primary producers], environmental factors (water chemistry parameters), biotic interactions, shared variance, and unexplained variance. The total explained variance reached 39.4% and the largest proportion of this explained variance was attributed to msPAF (23.7%). When each group (phytoplankton, zooplankton and macroinvertebrates) was analysed separately, biota interactions and environmental factors explained the largest proportion of variance. Results of this study indicate that besides the presence of pesticide mixtures, environmental factors and biotic interactions also considerably influence field freshwater communities. Subsequently, to increase our understanding of the risk of pesticide mixtures on ecosystem communities in edge-of-field water bodies, variations in environmental and biological factors should also be considered.

Ecological risk assessment of imidacloprid applied to experimental rice fields: Accurateness of the RICEWQ model and effects on ecosystem structure.

The fate of imidacloprid and its potential side-effects on biological communities and ecosystem functioning was studied in experimental rice plots. In addition, the influence of applying a withholding period of zero days (actual practices) and seven days (recommended in EU) on this was evaluated. Predicted environmental concentrations (PEC) of imidacloprid calculated with the higher-tier model RICEWQ agreed well with concentrations measured in the field. Methodologies generally used in the EU and USA for lower-tier PEC calculation, however, severely underestimated actual field concentrations and hence appear to need further evaluation and eventually amendments. Effects on several biological communities (especially ostracods, dipterans and coleopterans) were noted following imidacloprid application, with greatest effects in the paddy were as applied a withholding period of 7 days. An increase in the density of snails (Physa acuta), however, may have prevented effects on ecosystem functioning through functional redundancy. Implications of study findings for the ecological risk assessment of imidacloprid and potential mitigation measures are discussed.

Comparing ecotoxicological standards of plant protection products potentially toxic to groundwater life with their measured and modelled concentrations.

Trigger values (TVs) for groundwater ecosystems in the European Union (EU), as elsewhere, are not based on toxicity data for the biota of that ecosystem. At present, very few toxicity tests have been conducted with groundwater organisms so the true sensitivity of groundwater ecosystems is largely unknown. In a previous published study, we set groundwater TVs for all plant protection products (PPPs) allowed for use at the time of the study based on toxicity data for surface water organisms as surrogates for groundwater organisms and calculated TVs lower than the current EU standard of 0.1 µg/L for 16 PPPs. This thus reveals that the effect assessment of these PPPs may not be fully adequate, but would still only indicate risk if the (expected) concentrations of these PPPs are greater than their calculated TVs. The present study was therefore initiated to evaluate whether predicted and measured concentrations of these PPPs are higher than the previously calculated TVs lower than 0.1 µg/L. To this end, predicted environmental concentrations (PECs) were calculated using the PELMO and SCI-GROW models that are currently used for this purpose in the EU and USA, respectively, and measured concentrations (MECs) were obtained from the open literature. In addition, the empirical PERPEST model was used to assess the severity and probability of effects that may be expected at these concentrations on taxonomic groups known to be well represented in groundwater ecosystems. In addition, only for dimethoate a PEC greater than 0.1 µg/L was calculated. However, when considering concentrations actually measured in the field, 99.7% showed risk quotients (RQ, as MEC/TV) values higher than 1 and 36.7% even higher than 100. Future field monitoring studies are needed to validate and eventually calibrate the way PEC values are currently calculated with the different models and scenarios currently in use. Such studies would also aid in the question to what extent the high MEC values may be attributed to diffuse or point-source pollution.

Toxicity of environmentally realistic concentrations of chlorpyrifos and terbuthylazine in indoor microcosms.

Few studies have been conducted into the evaluation of environmentally realistic pesticide mixtures using model ecosystems. In the present study, the effects of single and combined environmentally realistic concentrations of the herbicide terbuthylazine and the insecticide chlorpyrifos were evaluated using laboratory microcosms. Direct toxic effects of chlorpyrifos were noted on copepod nauplii and cladocerans and the recovery of the latter was likely related with the decrease observed in rotifer abundances. Terbuthylazine potentiated the effect of chlorpyrifos on feeding rates of Daphnia magna, presumably by triggering the transformation of chlorpyrifos to more toxic oxon-analogs. Possible food-web interactions resulting from multiple chemical (and other) stressors likely to be present in edge-of-field water bodies need to be further evaluated.

Evaluation of FOCUS surface water pesticide concentration predictions and risk assessment of field-measured pesticide mixtures-a crop-based approach under Mediterranean conditions.

FOCUS models are used in the European regulatory risk assessment (RA) to predict individual pesticide concentrations in edge-of-field surface waters. The scenarios used in higher tier FOCUS simulations were mainly based on Central/North European, and work is needed to underpin the validity of simulated exposure profiles for Mediterranean agroecosystems. In addition, the RA of chemicals are traditionally evaluated on the basis of single substances although freshwater life is generally exposed to a multitude of pesticides. In the present study, we monitored 19 pesticides in surface waters of five locations in the Portuguese 'Lezíria do Tejo' agricultural area. FOCUS step 3 simulations were performed for the South European scenarios to estimate predicted environmental concentrations (PECs). We verified that 44% of the PECs underestimated the measured environmental concentrations (MEC) of the pesticides, showing a non-compliance with the field data. Risk was assessed by comparing the environmental quality standards (EQS) and regulatory acceptable concentrations with their respective MECs. Risk of mixtures was demonstrated in 100% of the samples with insecticides accounting for 60% of the total risk identified. The overall link between the RA and the actual situation in the field must be considerably strengthened, and field studies on pesticide exposure and effects should be carried out to assist the improvement of predictive approaches used for regulatory purposes.