An in situ assay with the microalga Phaeodactylum tricornutum for sediment-overlying water toxicity evaluations in estuaries.

Given the urgent need for ecologically relevant toxicity tools specific to estuarine systems, the main goal of the present study was to develop and evaluate the potential of an in situ algal assay for estuarine sediment-overlying water toxicity evaluations using the microalga Phaeodactylum tricornutum immobilized in alginate beads. With its simple and cost-effective design, the assay apparatus, coupled with the use of microalgae immobilized in alginate beads, allowed rapid and easy deployment as well as retrieval of assay chambers. The effectiveness of the proposed in situ assay was investigated by deploying it at two reference and six contaminated Portuguese estuaries. By deploying open chambers both with and without an artificial nutrient source and closed chambers with an artificial seawater medium, it was possible to discriminate toxic effects from those caused by differences in temperature, light, and nutrient conditions across sites. A reduction in algal growth was found at contaminated sites relative to reference sites. The strontium alginate beads used for microalgae immobilization were found to be appropriate to perform in situ assays, showing no signs of disruption or dissolution after up to 8 d of exposure in estuarine sediment-overlying waters. The proposed in situ assay was shown to be a useful tool for estuarine sediment-overlying water toxicity testing to provide relevant data concerning primary production to estuarine ecological risk assessment studies.