Neonicotinoids are prophylactically used globally on a variety of crops, and there is concern for the potential impacts of neonicotinoids on aquatic ecosystems. The intensive use of pesticides on crops has been identified as a contributor to population declines of amphibians, but currently little is known regarding the sublethal effects of chronic neonicotinoid exposure on amphibians. The objective of the present study was to characterize the sublethal effect(s) of exposure to 3 environmentally relevant concentrations (1 mg/L, 10 mg/L, and 100 mg/L) of 2 neonicotinoids on larval wood frogs (Lithobates sylvaticus) using outdoor mesocosms. We exposed tadpoles to solutions of 2 commercial formulations containing imidacloprid and thiamethoxam, and assessed survival, growth, and development. Exposure to imidacloprid at 10 mg/L and 100 mg/L increased survival and delayed completion of metamorphosis compared with controls. Exposure to thiamethoxam did not influence amphibian responses. There was no significant effect of any treatment on body mass or size of the metamorphs. The results suggest that current usage of imidacloprid and thiamethoxam does not pose a threat to wood frogs. However, further assessment of both direct and indirect effects on subtle sublethal endpoints, and the influence of multiple interacting stressors at various life stages, is needed to fully understand the effects of neonicotinoids on amphibians.

Polar organic chemical integrative samplers (POCIS) were used to estimate atrazine contamination at 24 stream/river sites located across a watershed with land use ranging from 6.7 to 97.4% annual crops and surface water nitrate concentrations ranging from 3 to 5404 μg/L. A gradient of atrazine contamination spanning two orders of magnitude was observed over two POCIS deployments of 28 d and was positively correlated with measures of agricultural intensity. The metabolite desisopropyl atrazine was used as a performance reference compound in field calibration studies. Sampling rates were similar between field sites but differed seasonally. Temperature had a significant effect on sampling rates while other environmental variables, including water velocity, appeared to have no effect on sampling rates. A performance reference compound approach showed potential in evaluating spatial and temporal differences in field sampling rates and as a tool for further understanding processes governing uptake of polar compounds by POCIS.

Intensification of agriculture and the corresponding increase in herbicide use has led to concern regarding the effects these chemicals may have on nontarget plants of agroecosystems. Current pesticide registration guidelines are focused on testing crop species grown singly in pots under greenhouse conditions and may not provide adequate measures of protection to noncrop species. The objective of the present study was to compare the response of terrestrial and wetland plants to the herbicides glyphosate and atrazine when grown singly in pots versus under different microcosm conditions. Greenhouse microcosms were generally more sensitive than single-species tests. Plants grown for an extended test period or in seminatural field conditions were generally less sensitive to herbicides. Sensitivity was found to be dependent on interactions between species and test conditions. Changes in community structure were observed in herbicide-treated microcosms that would not be predicted from single-species testing. Single-species tests are useful because they are inexpensive, can demonstrate clear dose-response patterns uncomplicated by other factors influencing growth, and are able to provide a measure of the sensitivity of a given species to glyphosate and atrazine. However, they are unable to predict subtle changes in community structure that may have important long-term consequences.

Agrochemicals, including fertilizers and herbicides, are significant contributors of non-point source pollution to surface waters and have the potential to negatively affect periphyton. We characterized periphyton communities using pigment markers to assess the effects of nutrient enrichment and the herbicide atrazine with in situ experimental manipulations and by examining changes in community structure along existing agrochemical gradients. In 2008, the addition of nutrients (20 mg/L nitrate and 1.25 mg/L reactive phosphate), atrazine (20 μg/L) and a combination of both nutrients and atrazine had no significant effect on periphyton biomass or community structure in a stream periphytometer experiment. In 2009, similar experiments with higher concentrations of atrazine (200 μg/L) at two stream sites led to some minor effects. In contrast, at the watershed scale (2010) periphyton biomass (mg/m(2) chlorophyll a) increased significantly along correlated gradients of nitrate and atrazine but no direct effects of reactive phosphate were observed. Across the watershed, the average periphyton community was composed of Bacillariophyceae (60.9%), Chlorophyceae (28.1%), Cryptophyceae (6.9%) and Euglenophyceae (4.1%), with the Bacillariophyceae associated with high turbidity and the Chlorophyceae with nitrate enrichment. Overall, effects of nitrate on periphyton biomass and community structure superseded effects of reactive phosphate and atrazine.