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

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. • The three sulfur mustard metabolites had no significant impact on algal growth rate. • TNT, tetryl, and 1,3-DNB caused strong growth inhibition at environmentally relevant concentrations. • Picric acid induced a hormetic response, with growth stimulation at exposed concentrations. • Results support risk-based prioritization of nitroaromatic explosives at munition dumpsites.