AWWA MTC95010

Common ion toxicity is implicated in several failed whole effluent toxicity tests dealing with membrane concentrate in Florida. It is a type of toxicity different from that due to toxic substances such as heavy metals, pesticides, etc. Rather it is associated with common ions such as: sodium, potassium, calcium, magnesium, strontium, chloride, sulfate, bicarbonate, borate, and bromide. It appears to occur where the proportions of these substances are different from those found in natural seawater. Due to many unknowns associated with common ion toxicity, the Florida Department of Environmental Protection is taking a cautious approach to dealing with the cases of failed WET tests. Currently, several membrane utilities are operating under temporary operating permits until the situation is better understood. Common ion toxicity has occurred in many different locations in the United States in other industries. It is thus a matter of times before membrane facilities in other states encounter this same situation. This paper presents information about common ion toxicity and discusses: what it is; what is known about it; where it occurs; what research has been conducted; the regulatory situation in Florida that involves it; recommendations for further work. It is important that the phenomenon is well understood and that appropriate regulations are developed that are scientifically based.