Many environments are subject to periodic fluctuations in pollutant concentrations. Passive samplers, which can provide time weighted average concentrations integrated over the period of deployment, are ideally suited as monitoring tools for these environments. However, the potential for fluctuating concentrations to limit the integrative period of sampling needs to be investigated before sampling data from these environments can be interpreted with confidence. In this study, Chemcatchers using SDB-RPS Empore disks as the sorbent phase were exposed to herbicides for 28 days in a calibration chamber. A pulsed event of 10-fold greater concentrations was introduced on day 5 and returned to background concentrations over a period of 3 days. Observed uptake was compared with that predicted by a first order uptake model and by the reduced form of this model describing a strictly integrative response for samplers deployed with two surfaces exposed (two-sided naked), with one surface exposed (one-sided naked) and with a polyethersulfone membrane. Membrane covered samplers predicted time weighted average water concentrations within a factor 0.7-1.2 after 28 days exposure, while one- and two-sided naked samplers under predicted the average by a factor 1.9-2.2 and 2.4-3.2, respectively. First order modeling predicted uptake in membrane covered and one-sided naked samplers and was therefore applied to predict sampler response to several fluctuating concentration event scenarios.
This special issue presents a collection of papers covering the environmental fate, effects, and risk of pesticides in tropical environments, which is expected to facilitate improved management of pesticides. Environmental monitoring programs of surface and ground waters in the tropics, including areas of high ecological value, have detected several relatively polar pesticides at concentrations that are of ecological concern. Novel monitoring techniques have the capacity to reveal the spatial and temporal extent of such risks. To best manage these pesticides, their sorption, dissipation rates, leaching, and runoff potential need to be better understood. On these aspects, important insights have been provided by several studies within this issue. Improved understanding of the environmental fate, effects, and risks through studies presented in this special issue is crucial for minimizing the nontarget impacts of pesticides on biodiversity-rich tropical regions.
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