Application of a programmed semi-automated Ulva pertusa bioassay for testing single toxicants and stream water quality

A toxicity test based on inhibition of reproduction in the green macroalga Ulva pertusa involves quantifying the change in thallus color as reproduction progresses. However, interpretation of this color change is reliant on the skill level of the examiner. This study aimed to validate a new toxicity test based on inhibition of reproduction in the green macroalga U. pertusa using a vital stain and programmed semi-automated analysis (using Image J) of the change in thallus color. The toxicity rank by inverse EC₅₀ values was: irgarol (0.048 mg L^-1) > Ag (0.132 mg L^-1) > As (0.172 mg L^-1) > simazine (0.378 mg L^-1) > formaldehyde (0.442 mg L^-1) > DCOIT (0.783 mg L^-1) > ZnPT (3.556 mg L^-1) > medetomidine (11.600 mg L^-1) > phenol (29.316 mg L^-1) > methanol (2,736 mg L^-1) > ethanol (3,306 mg L^-1). The sensitivity of the U. pertusa test to stream waters was similar to or lower than those of the commonly-used Lemna minor and Daphnia magna bioassays. The U. pertusa bioassay is sensitive to, and suitable for, testing various toxicants including metals, volatile organic compounds, herbicide, antifouling agents and phenol and can also be applied to testing freshwater quality after salinity adjustment.