Uptake and Depuration of 4-Nonylphenol by the Benthic Invertebrate Gammarus pulex: How Important Is Feeding Rate?

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Abstract
The major exposure and uptake route for soluble toxins by aquatic organisms is generally considered to be through the water column. In the case of hydrophobic chemicals, exposure and uptake through diet often take on greater importance as the chemicals adsorb onto organic sediments and food. A chemical that has recently come under close scrutiny because of its toxicity and possible endocrine disrupting effects in aquatic life is 4-nonylphenol (NP). It has been detected in environmental water and sediment samples and is a persistent and hydrophobic (log Kow = 4.48) contaminant in many aquatic systems. In this study, the relative importance of NP uptake through accumulation from diet and water was examined for the detritus-feeding freshwater shrimp Gammarus pulex. Using a bootstrap nonlinear regression technique, the level of toxin present in G. pulex at any time during or after initial exposure was estimated. Heterogeneity, together with assumptions on feeding rate, was shown to affect the determination of NP uptake substantially. Because of its lifestyle as a benthic organism, the main exposure route was at first assumed to be through sediments and food. However, the results suggest that major uptake may also occur through water. The statistical and modeling methodology may be applied to uptake and depuration assessments for any aquatic organisms exhibiting a variable feeding phase.

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