ABSTRACT
Agricultural pesticides are used intensively during the spring and summer, which coincides with the spawning and sensitive early life stages of many estuarine species as well as marine species that spawn in the estuary. It is often difficult to prove that elevated concentrations of xenobiotic chemicals cause effects on the estuarine ecosystem. As the river widens into the estuary, however, the water energy decreases and sediments, with adsorbed contaminants, settle in estuarine areas with little tidal or wave movement. Chemical contaminants entering the estuary are partitioned into the water column, suspended matter, sediments, and organisms. Pharmacokinetic models can be used to study uptake from food and water, metabolic conversions, bioaccumulation, and excretion. In salt marshes the plants can act as pumps to draw nutrients out of the substrate and into the water column. Impaired reproduction has been shown in top carnivores such as marine mammals and birds following exposure to high levels of toxic substances.
