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Ecological risk assessment (ERA) has followed a taxonomy-based approach, making the assumption that related species will show similar sensitivity to toxicants, and using safety factors or species sensitivity distributions to extrapolate from tested to untested species. In ecology it has become apparent that taxonomic approaches may have limitations for the description and understanding of species assemblages in nature. Therefore it has been proposed that the inclusion of species traits in ERA could provide a useful and alternative description of the systems under investigation. At the same time, there is a growing recognition that the use of mechanistic approaches in ERA, including conceptual and quantitative models, may improve predictive and extrapolative power. Purposefully linking traits with mechanistic effect models could add value to taxonomy-based ERA by improving our understanding of how structural and functional system facets may facilitate inter-species extrapolation. Here, we explore whether and in what ways traits can be linked purposefully to mechanistic effect models to predict intrinsic sensitivity using available data on the acute sensitivity and toxicokinetics of a range of freshwater arthropods exposed to chlorpyrifos. The results of a quantitative linking of seven different endpoints and twelve traits demonstrate that while quantitative links between traits and/or trait combinations and process based (toxicokinetic) model parameters can be established, the use of simple traits to predict classical sensitivity endpoints yields little insight. Remarkably, neither of the standard sensitivity values, i.e. the LC(50) or EC(50), showed a strong correlation with traits. Future research in this area should include a quantitative linking of toxicodynamic parameter estimations and physiological traits, and requires further consideration of how mechanistic trait-process/parameter links can be used for prediction of intrinsic sensitivity across species for different substances in ERA.

Under typical agricultural use of an insecticide, it is likely that only part of an edge-of-field drainage ditch will be directly contaminated by spray drift. The response, including recovery, of aquatic macroinvertebrates in sprayed ditch sections may be affected by immigration of organisms from adjacent nonsprayed ditch sections, but also the population dynamics in nonsprayed sections (refuges) may be affected by nearby contaminated patches (known as action at a distance). Experimental ditches were used to study the influence of the presence of nearby refuges on the responses of macroinvertebrates in ditch sections directly sprayed with the insecticide lufenuron, and vice versa. The treatment regimes differed in the proportion of the ditch (0, 33, 67, and 100% of surface area) that was sprayed to reach a lufenuron concentration of 3 microg/L in the water column of the sprayed ditch section. In sprayed ditch sections, clear treatment-related effects were observed for adult midges in the emergence traps and for aquatic arthropods (mainly juveniles) in the artificial substrate/sweep net samples. The extent in magnitude and duration of effects in sprayed ditch sections was overall larger when a larger proportion of the ditch was sprayed and/or the distance to the refuge was larger. In nonsprayed ditch sections of partially treated ditches, treatment-related effects were absent or minor for macroinvertebrates that predominantly dwell on or in the sediment compartment, particularly at a larger distance from the sprayed ditch sections. More mobile arthropods that predominantly dwell in the water column showed clear treatment-related effects in the nonsprayed ditch sections as well, but action at a distance was smaller if a smaller proportion of ditch was treated., (Copyright 2010 SETAC.)

The long-term response, including recovery, of aquatic macroinvertebrates to short-term insecticide exposure may be affected by the presence of uncontaminated refuges in the stressed ecosystem. Experimental ditches were used to study the influence of non-sprayed ditch sections regarding the ecotoxicological effects on and the recovery of macroinvertebrates following treatment with the insecticide lufenuron. The treatment regimes differed in the proportion of the ditch (0, 33, 67, and 100% of surface area) that was sprayed to reach a lufenuron concentration of 3 microg/L in the water column of the sprayed ditch section. The magnitude and duration of effects on macroinvertebrates, and on arthropods in particular, were higher when a larger proportion of the ditch was treated. Initially, more pronounced responses were observed for bivoltine and multivoltine insects and macrocrustaceans than for univoltine and semivoltine arthropods. Most macroinvertebrate arthropods showed delayed responses, with maximum treatment-related effects observed two to six weeks after lufenuron application. This latency of effects can be explained by the mode of action of lufenuron, involving inhibition of chitin synthesis, which affects arthropod molting and metamorphosis. The observed effects were short-lived only in those ditches where 33% of the surface area was sprayed. In the ditches where 67 and 100% of the surface area was sprayed, some insects and macrocrustaceans showed long-term effects. In the 100% sprayed ditches in particular, the treatment-related reduction in arthropods resulted in indirect effects, such as an increase in snails, and later in an increase in the ephemeropteran Cloeon dipterum, probably because of an increase in periphyton, and release from competition and predation. Effects that are most likely indirect also were observed for Oligochaeta, Hirudinea, and the flatworm Mesostoma sp.

The aim of the study was to compare the effects of the pyrethroid insecticide lambda-cyhalothrin (treated at 10, 25, 50, 100, 250 ng active ingredient a.i./L) on a drainage ditch ecosystem in spring and late summer. Microcosms (water volume approximately 430 L) were established using enclosures in a 50-cm-deep experimental ditch system containing communities typical of macrophyte-dominated freshwater ecosystems. Effects on macroinvertebrates, zooplankton, phytoplankton, macrophytes, and community metabolism were assessed and evaluated using univariate and multivariate statistical techniques. The macroinvertebrate community responded most clearly to treatment and, as anticipated, insects and crustaceans were among the most sensitive organisms. Statistical analysis showed that the underlying community structure was significantly different between the spring and summer experiments. However, the most sensitive species (Chaoborus obscuripes and Gammarus pulex) were abundant in spring as well as in late summer. In spring and late summer, only slight and transient effects were observed at the community level in the 10-ng/L treatment. Overall, the study did not show substantial differences in the responses of sensitive taxa between spring and late summer treatments, and effects thresholds were similar irrespective of season of treatment.

The toxicity of the pyrethroid insecticide lambda-cyhalothrin to freshwater invertebrates has been investigated using data from short-term laboratory toxicity tests and in situ bioassays and population-level effects in field microcosms. In laboratory tests, patterns of toxicity were consistent with previous data on pyrethroids. The midge Chaoborus obscuripes was most sensitive (48- and 96-h EC50 = 2.8 ng/L). Other insect larvae (Hemiptera, Ephemeroptera) and macrocrustacea (Amphipoda, Isopoda) were also relatively sensitive, with 48- and 96-h EC50 values between 10 and 100 ng/L. Generally, microcrustacea (Cladocera, Copepoda) and larvae of certain insect groups (Odonata and Chironomidae) were less sensitive, with 48-h EC50 values higher than 100 ng/L. Mollusca and Plathelminthes were insensitive and were unaffected at concentrations at and above the water solubility (5 microg/L). Generally, the EC50 values based on initial population responses in field enclosures were similar to values derived from laboratory tests with the same taxa. Also, the corresponding fifth and tenth percentile hazard concentrations (HC5 and HC10) were similar (laboratory HC5 = 2.7 ng/L and field HC5 = 4.1 ng/L; laboratory and field HC10 = 5.1 ng/L), at least when based on the same sensitive taxonomic groups (insects and crustaceans) and when a similar concentration range was taken into account. In the three field enclosure experiments and at a treatment level of 10 ng/L, consistent effects were observed for only one population (Chaoborus obscuripes), with recovery taking place within 3 to 6 weeks. The laboratory HC5 (2.7 ng/L) and HC10 (5.1 ng/L) based on acute EC50 values of all aquatic arthropod taxa were both lower than this 10 ng/L, a concentration that might represent the "regulatory acceptable concentration." The HC5 and HC10 values in this study in The Netherlands (based on static laboratory tests with freshwater arthropods) were very similar to those derived from a previous study in the United Kingdom (1.4 and 3.3 ng/L). This suggests that for pesticides like lambda-cyhalothrin, HC5 values based on static laboratory tests may provide a conservative estimate of the potential for community-level effects under field conditions. While these HC5 values are conservative for initial effects, they do not provide information on recovery potential, which may be important for regulatory decision-making.

The growth of the freshwater macroinvertebrates Gammarus pulex (L.) and Chironomus riparius Meigen exposed to 3,4-dichloroaniline in chambers within stream mesocosms was determined. DCA significantly affected the growth of neonate G. pulex and third instar C. riparius over 25 and 12 days, respectively. The no-observed-effect concentrations (NOECs) obtained in the tests were 0.08 mg DCA liter-1 (G. pulex) and 0.76 mg DCA liter-1 (C. riparius) and these are compared to toxicity data from other investigations. Inclusion of single-species bioassays in mesocosm studies provides complementary information on toxicant effects and indicates the suitability of the results of such tests (which may be routinely performed under laboratory conditions) for protecting particular ecosystems.