The cytotoxic drug, cisplatin (cis-PtCl(2)(NH(3))(2)), has been added to cultures of the marine macroalga, Ulva lactuca, under various experimental conditions. Both accumulation and internalisation over a 48 h period was greater when cisplatin was added to coastal sea water (salinity = 33) from a distilled water solution than when added to either sea water or estuarine water (salinity = 16.5) from a saline solution. This effect is attributed to the greater abundance of the more reactive monoaqua complex (cis-PtCl(OH(2))(NH(3))(2)(+)) in the distilled water solution and kinetic constraints on its conversion back to cis-PtCl(2)(NH(3))(2) in sea water. Despite its mode of action at the cellular level, cisplatin added up to concentrations of 150 nM did not incur a measurable reduction in the efficiency of photochemical energy conversion under any of experimental conditions tested. Copyright © 2011 Elsevier Ltd. All rights reserved.