Photosynthesis tests as an alternative to growth tests for hazard assessment of toxicant

Acute (3- and 6-h) toxic responses toward Cu, linear alkylbenzene sulfonate (LAS), and tributyltin (TBT) of lightsaturated and unsaturated photosynthesis were investigated for Rhodomonas salina and Skeletonema costatum obtained from exponentially growing batch cultures and from chemostat cultures limited by either nitrogen or phosphorus. The sensitivity of the photosynthesis tests were compared to standardized growth tests applied to the same species and toxicants. For Cu and S. costatum the photosynthesis test was up to 300 times more sensitive at light saturation than at light limitation. For the remaining photosynthesis tests no dependence on light condition were found. The photosynthesis tests with Cu and S. costatum were up to 10 times as sensitive as the growth test and most sensitive when the algae were obtained from a phosphatelimited chemostate. For the other photosynthesis tests no dependence on the growth condition were found, and the photosynthesis tests were as sensitive as the growth test. Photosynthesis tests offer an alternative to growth tests for hazard assessment of toxicants.