BackgroundMixtures of organophosphate and carbamate pesticides are commonly detected in freshwater habitats that support threatened and endangered species of Pacific salmon (Oncorhynchus sp.). These pesticides inhibit the activity of acetylcholinesterase (AChE) and thus have potential to interfere with behaviors that may be essential for salmon survival. Although the effects of individual anticholin-esterase insecticides on aquatic species have been studied for decades, the neurotoxicity of mixtures is still poorly understood.ObjectivesWe assessed whether chemicals in a mixture act in isolation (resulting in additive AChE inhibition) or whether components interact to produce either antagonistic or synergistic toxicity.MethodsWe measured brain AChE inhibition in juvenile coho salmon (Oncorhynchus kisutch) exposed to sublethal concentrations of the organophosphates diazinon, malathion, and chlorpyrifos, as well as the carbamates carbaryl and carbofuran. Concentrations of individual chemicals were normalized to their respective median effective concentrations (EC50) and collectively fit to a nonlinear regression. We used this curve to determine whether toxicologic responses to binary mixtures were additive, antagonistic, or synergistic.ResultsWe observed addition and synergism, with a greater degree of synergism at higher exposure concentrations. Several combinations of organophosphates were lethal at concentrations that were sublethal in single-chemical trials.ConclusionSingle-chemical risk assessments are likely to underestimate the impacts of these insecticides on salmon in river systems where mixtures occur. Moreover, mixtures of pesticides that have been commonly reported in salmon habitats may pose a more important challenge for species recovery than previously anticipated.

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The performance of polyvinyl chloride polymer (PVC) dispensers loaded with two rates of ethyl (E,Z)‐2,4‐decadienoate (pear ester) plus the sex pheromone, (E,E)‐8,10‐dodecadien‐1‐ol (codlemone) of codling moth, Cydia pomonella (L.), was compared with similar dispensers and two commercial dispensers (Isomate® and CheckMate®) loaded only with codlemone. Dispenser evaluations were conducted in replicated small (0.1 ha) and large (2 ha) field trials in apple, Malus domestica (Borkhausen), during 2006 (Washington) and 2007 (Michigan, large plot study only). Data recorded included male captures in traps baited with virgin female moths and codlemone lures and direct observations of moth behaviour in treated plots. Volatile air collections of field‐aged dispensers were conducted under laboratory conditions. Disruption of male catch in codlemone‐baited traps was generally similar among dispenser treatments, except for two instances: lower moth catches with the single and dual‐component PVC dispensers, compared with Isomate®, during the first flight in the large plots in Michigan in 2007 and for the dual‐component PVC dispenser compared with the CheckMate® dispenser during the second flight in small plots in Washington in 2006. Levels of fruit injury were similar in large plots treated with all dispensers. Male moth catches in virgin female‐baited traps did not differ among dispenser treatments and were significantly lower than the untreated control. Behavioural observations of adult moths in the field verified anemotactic approaches within 20 cm of pheromone dispensers loaded with and without pear ester that lasted ca. 15 s on average. Field‐aged dual‐component dispensers released pear ester at a >5‐fold higher rate than codlemone over the first 8 weeks and this ratio declined to near unity by 18 weeks.

This study characterized exposures of eight children living in an agricultural community near potato fields that were treated by aerial application with the organophosphorus (OP) insecticide, methamidophos (O,S-dimethyl phosphoramidothioate). Exposure monitoring included air and deposition samples in the outdoor community environment, outdoor and indoor air samples at each residence, wipe samples of playground equipment, toys, indoor surfaces, and children's hands, and periodic urine samples. Monitoring occurred prior to, the day of, and 1 day following applications. Methamidophos deposition in the community was very low compared to deposition inside the boundaries of the treated fields. Community air concentrations increased from 0.05 mg/ m 3 (prespray) to 0.11 and 0.48 mg/m 3 (spray day morning and afternoon, respectively), decreasing to 0.10 mg/m 3 on the postspray day. Air concentrations outside residences followed a similar pattern; indoor levels did not exceed 0.03 pg/m 3 . Methamidophos residues were found on playground equipment following applications, but not on indoor residential surfaces. The median hand wipe levels increased from o0.02 (prespray) to 0.08 mg/sample (spray day), decreasing to 0.05 mg/sample (postspray day). Median concentrations of the primary methamidophos urinary metabolite were 61 mg/l before 1100 hours on the spray day, 170 mg/l after 1100 hours on the spray day, and 114 mg/l on the postspray day. Spray day metabolite levels were correlated with time outside on the spray day (r s ¼ 0.68), with spray day hand wipe levels (r s ¼ 0.67), and with postspray day metabolite levels (r s ¼ 0.64). Postspray day metabolites levels were also positively associated with postspray day hand wipe levels (r s ¼ 0.66). The documentation of children's exposure in this study does not necessarily mean that risks for these children were significantly altered, since nearly all children in the United States are exposed to some level of OP pesticides through dietary intake and other pathways. The association of metabolite levels with time spent outside, and the absence of methamidophos in homes indicates that children's exposures occurred primarily outdoors.