THE PHOTOSYNTHETIC RESPONSES OF MARINE-PHYTOPLANKTON, PERIPHYTON AND EPIPSAMMON TO THE HERBICIDES PARAQUAT AND SIMAZINE

Short-term toxicity tests using photosynthesis (incorporation of C-14) as a test parameter were performed in order to compare the sensitivit ies of three marine microalgal communities (phytoplankton, periphyton and epipsammon) to two herbicides, paraquat and simazine. Thirty minut es of pre-exposure to simazine were sufficient to obtain the full effe ct in all communities, while for paraquat 4 h was required. The bioava ilability of paraquat and simazine was not limited by adsorption to se diment in the epipsammon samples. Simazine was more toxic than paraqua t for the three communities at similar concentrations. Phytoplankton w as slightly more sensitive for both herbicides (EC50 ranges of 9-23 mu M for paraquat and 0.37-0.99 mu M for simazine) than periphyton and e pipsammon. These attached communities exhibited different results for each toxicant, periphyton being more sensitive to paraquat (EC50 range 9-21 mu M) and epipsammon to simazine (EC50 range 0.44-1.17 mu M). Th e three communities presented EC ranges comparable to those found in s ingle species tests, suggesting that different levels of biological or ganization can exhibit a similar sensibility to toxicants, thus indica ting that natural communities are suitable for use in these kinds of t oxicity tests.