Contrasting toxicity between explosives– and chemical warfare agents–related compounds to the marine primary producer <i>Phaeodactylum tricornutum</i>

Vast amounts of munitions dumped in the marine environment, have been reported to leak chemicals due to munition corrosion. The subsequent increased levels of explosives and related chemicals (E&RC), as well as chemical warfare agents and related chemicals (CWA&RC), raise risks for environmental and human health Yet, ecotoxicity data on primary producers is currently scarce. Therefore, this study investigated the acute effects of three CWA&RC (1,4-oxathiane, 1,4-dithiane, and thiodiglycol) and four E&RC (2,4,6-trinitrotoluene (TNT), tetryl, 1,3-dinitrobenzene (1,3-DNB), and picric acid) on Phaeodactylum tricornutum, a key marine diatom at the basis of the aquatic food web. Results showed that none of the three CWA&RC significantly inhibited the growth rate of Phaeodactylum tricornutum at the tested concentrations. Interestingly, picric acid stimulated growth up under the experimental conditions, suggesting a hormetic effect. TNT, tetryl, and 1,3-DNB strongly inhibited growth, with experimentally derived EC10 and EC50 values approaching environmentally relevant concentrations near dumpsites. Consequently, diatom biomass may be significantly affected by TNT, tetryl, and 1,3-DNB, potentially disturbing primary production and ocean chemistry. Future research should examine potential synergies between munition compounds and other marine pollutants, which may aggravate toxic effects, as well as consider long-term toxicity tests.