Major ion toxicity in effluents: A review with permitting recommendations

Effluent toxicity testing methods have been well defined, but for the most part, these methods do not attempt to segregate the effects of active ionic concentrations and ion imbalances upon test and species performances. The role of various total dissolved solids in effluents on regulatory complianc e has emerged during the last few years and has caused confusion in technic al assessment and in permitting and compliance issues. This paper assesses the issue of ionic strength and ion imbalance, provides a brief summary of applicable data, presents several case studies demonstrating successful too ls to address toxicity resulting from salinity and ion imbalance, and provi des recommendations for regulatory and compliance options to manage dischar ges with salinity/ion imbalance issues. Effluent toxicity resulting from in organic ion imbalance and the ion concentration of the effluent is pervasiv e in permitted discharge from many industrial process and municipal dischar ges where process streams are concentrated, adjusted, or modified. This pap er discusses procedures that use weight-of-evidence approaches to identify ion imbalance toxicity, including direct measurement, predictive toxicity m odels for freshwater. exchange resins, mock effluents, and ion imbalance to xicity with tolerant/susceptible text species. Cost-effective waste treatme nt control options for a facility whose effluent is toxic because of total dissolved solids (TDS) or because of specific ion(s) are scarce at best. De pending on the discharge situation, TDS toxicity may not be viewed with the same level of concern as other, more traditional, toxicants. These dischar ge situations often do not require the conservative safety factors required by other toxicants. Selection of the alternative regulatory solutions disc ussed in this paper may be beneficial, especially because they do not requi re potentially expensive or high-energy-using treatment options that may be ineffective control options. The information presented is intended to prov ide a better understanding of the role of ion imbalance in aquatic toxicity testing and to provide various recommendations that should be considered i n addressing these issues.