Pick your poison: do cyanotoxins or disinfection by-products pose the greater risk?

Cyanobacterial toxins continue to pose an environmental problem, but from a drinking water perspective, the toxin-containing cells are readily removed during flocculation and filtration in water treatment, and chlorine is able to degrade residual dissolved toxins. However, with the addition of chlorine, dissolved organic carbon compounds in the source water are oxidised to form halogenated organic compounds known as disinfection by-products (DBPs). From a human health perspective, the risk has therefore shifted from cyanotoxins, which can be degraded with chlorine, to DBPs from algal-derived precursors. This shift should be accompanied by a focus on better understanding DBP precursors from algae and the epidemiology of long-term exposure to them.