Measuring “total” contaminant concentrations doesn’t always tell us about the portion that is actually able to be taken up by an organism (bioavailable). It is this bioavailable portion that is potentially toxic. Contaminant concentrations in aquatic organisms such as shellfish have been widely used as a direct measure of the bioavailable portion. However, high natural variability and cost have led to the search for methods which provide more consistent (and hence reliable) results at lower costs. PSDs have this potential, but their effectiveness hadn’t been demonstrated in NZ. A recent publication in NZ Journal Of Marine and Freshwater Research provides evidence that PSDs have enormous potential as shellfish surrogates. A NZ-wide team led by Dr Mike Stewart (SEL) assessed the suitability of three different PSDs for measuring urban heavy metals, along with current and emerging organic contaminants. Could PSDs replace shellfish monitoring? The short answer is that it is too early to say, but PSDs show enormous potential as shellfish surrogates.