The Synergy between Herbicides, Oil and Solvents in Bio-Toxicity to Phaeodactylum tricornutum Bohlin-Implications for Interpretation of Field Sample Data

Bioassays of the herbicides Simazine and Atrazine, alone and as cocktails with oil and solvents were performed by a modified ISO 10253 1995 bio-toxicity test, with the test diatom Phaeodactylum tricornutum Bohlin. This laboratory bioassay was necessary to interpret pollutant data from field studies in the Northern Black Sea.

The present study establishes the sensitivity of the test organism to these pollutants in different combinations. Cultures of the test alga were exposed to dilution series of ethanol, DMSO, oil, Atrazine and Simazine. Ethanol was toxic to the diatoms at concentrations 100 times below DMSO, which was therefore used in the following tests, in a safe concentration (0.03% v/v).

The oil (up to 10% v/v) alone was not significantly toxic, but with DMSO it was moderately toxic at concentrations ≥ 0.032% (v/v). The algal growth after 2-4 days was significantly reduced by ≥ 0.1 mg L-1 of Atrazine or Simazine in 0.03% v/v DMSO. The presence of oil and DMSO increased herbicide toxicity to the algae. The effective concentrations for the bio-test are far above the ecologically relevant concentrations of the pollutants found in most natural waters. The data suggest, however, that in the interpretation of algal bioassays of field water samples, the impact of synergy between different pollutants in pollutant cocktails should be considered.