Do UK coastal and estuarine water samples pose a phototoxic threat?

► Marine water samples screened for phototoxic activity with the oyster embryo bioassay. ► Subsurface and sea surface microlayer samples analysed from 18 different locations. ► Majority of samples failed to display any phototoxic potential. ► Where phototoxic activity observed higher molecular weight PAHs also detected. ► Findings suggest phototoxicity should be considered where PAH contamination occurs.