Wastewater effects on Phaeodactylum tricornutum (Bohlin): Setting up a classification system

Phytoplankton is highly productive in marine coastal ecosystems that generally present high levels of anthropogenic pressures. Microalgae presents very high surface-to-volume ratio and may respond promptly to contaminants showing either an increase in growth or inhibition effects. Thus phytoplankton organisms provide information on the potential impacts of contaminants on the supported marine-coastal food webs. The diatom Phaeodactylum tricornutum Bohlin is commonly used in toxicity testing according to the ISO 10253:2006 standardised protocol, but a comprehensive inventory of tested substances has not been compiled yet. The aim of this study is to establish a wastewater effect score based on P. tricornutum exposed to domestic, municipal and industrial wastewaters from activated sludge sequencing batch reactor and ultra-filtration membrane biological reactors. Wastewater samples produced stimulation and inhibition effects identified by biostimulation unit (BU<inf>50</inf>) and toxicity unit (TU<inf>50</inf>) both at 50% effect, respectively. Within the stimulation scenario, toxicity was low if 0 < BU<inf>50</inf> ≤ 0.31, medium if 0.31 < BU;bsubesub ≤ 1.05, high if 1.05 < BU<inf>50</inf> ≤ 1.64, and very high if BU;bsubesub > 1.64. Within the inhibition scenario, toxicity was low if 0 < TU;bsubesub < 0.07, medium if 0.07 < TU<inf>50</inf> ≤ 2.67, high if 2.67 < TU;bsubesub ≤ 5.86, and very high if TU<inf>50</inf> > 5.86. Results evidenced that nitrogen and phosphorus concentrations were not correlated to ecotoxicological values, probably due to the presence of undetected micronutrients, confirming the importance of toxicity-based hazard assessment.