Three experiments were conducted to determine the impact of the insecticide chlorpyrifos (single applications of 0.01 to 10 microg AI litre(-1)) in plankton-dominated nutrient-rich microcosms. The microcosms (water volume approximately 14 litres) were established in the laboratory under temperature, light regimes and nutrient levels that simulated cool 'temperate' and warm 'Mediterranean' environmental conditions. The fate of chlorpyrifos in the water column was monitored and the effects on zooplankton, phytoplankton and community metabolism were followed for 4 or 5 weeks. The mean half-life (t1/2) of chlorpyrifos in the water of the test systems was 45 h under 'temperate' conditions and about 30 h under 'Mediterranean' environmental conditions. Microcrustaceans (cladocerans and copepod nauplii) were amongst the most sensitive organisms. All three experiments yielded community NOEC (no observed effect concentrations) of 0.1 microg AI litre(-1), similar to those derived from more complex outdoor studies. Above this threshold level, responses and effect chains, and time spans for recovery, differed between the experiments. For example, algal blooms as an indirect effect from the impact of exposure on grazing organisms were only observed under the 'Mediterranean' experimental conditions. The relatively simple indoor test system seems to be sufficient to provide estimates of safe threshold levels for the acute insecticidal effects of low-persistence compounds such as chlorpyrifos. The robustness of the community NOEC indicates that this threshold level is likely to be representative for many freshwater systems.
In a program of avian field studies, radiotelemetry was combined with observations, carcass searches, residue analysis, and determination of brain acetylcholinesterase (AChE) activity to assess the acute and short-term risk posed by chlorpyrifos to birds. Studies were conducted in field crops (brassicas, Poland) and orchards (pome, Italy; citrus, Spain). In total, 25 individual applications of chlorpyrifos were studied on 13 sites. Before each application, birds were fitted with radio transmitters (with minimum stress to birds). Radiotagged birds were monitored and the avifauna observed before, during and for 7 d following each application. A total of 201 birds representing 19 species were radiotagged. In 80% of individual telemetric monitoring periods, birds remained at the study sites. No radiotagged birds showed any sign of intoxication. These included individuals who spent a major proportion of time within treated areas (some individuals located within treated area on >90% of occasions). A total of 7,238 bird sightings were recorded during constant observation during and immediately after application. An additional 4,017 sightings were recorded in 104 individual surveys during 7 d after each application. Two untagged birds (out of 11,255 bird sightings) exhibited atypical behavior for <1 min and 2 to 3 min, respectively, before flying away. This observation (for 0.02% of bird sightings) may or may not have been treatment related. Ten carcasses were recovered (none radiotagged). Residue analysis and brain AChE activity indicated that none was likely to have died from chlorpyrifos exposure. Radiotracking, supported by more traditional assessment methods, was effective for assessing impacts in the field. This extensive field program supports a conclusion that spray applications of chlorpyrifos present a low risk to birds.
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