John Wiley & Sons, Ltd.

Defining an exposure‐response relationship for suspended kaolin clay particulates and aquatic organisms – work toward defining a water quality guideline for suspended solids

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Water quality guidelines for suspended solids generally rely on the percentage 'departure from reference condition', an approach that has been criticised. Attempts to develop a biological effects‐base guideline have, however, been confounded by low data availability. Furthermore, the high biological response variability to suspended solids exposure suggests organisms are responding not only to exposure concentration and duration but also to other mechanisms of effect associated with suspended particles (e.g. size, shape and geochemical composition). An alternative option is to develop more situation/site specific guidelines by generating biological effects data to suspended particles of a particular geochemistry and restricted size range. With this in mind, aquatic organism responses to kaolin clay particle exposure were collated from the literature and incorporated into two exposure‐response relationship approaches. The species sensitivity distribution approach produced an HC5 estimate of 58 mg/L for mortality responses, and of 36 mg/L for sub‐lethal data. The severity‐of‐ill‐effect approach produced similar estimates for lethal and sub‐lethal data. These results suggest that aquatic organisms are slightly more tolerant of kaolin clay particles than particles from barite or bentonite clays based on results from previous studies on these clay types. This type of information can enable better estimates of the risk faced by aquatic organisms exposed to suspended solids. For example, when the sediments of a particular water body are dominated by a particular type of clay particle then the most appropriate exposure‐response relationship can be applied. This article is protected by copyright. All rights reserved

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