IONIC IMBALANCE AS A SOURCE OF TOXICITY IN AN ESTUARINE EFFLUENT

A toxicity identification evaluation (TIE) was conducted on the efflue nt from a petrochemical plant which discharges into an estuary. The ef fluent had been consistently toxic to mysid shrimp (Mysidopsis bahia) but not toxic to sheepshead minnows (Cyprinodon variegatus). Phase I e ffluent toxicity characterization tests revealed that treatment of the effluent with a cation exchange resin (Amberlite(R) IR-120 Plus) was partially effective at reducing, but not removing, toxicity. Phase II characterization tests revealed that four cations varied with toxicity : Ca and Sn were positively correlated with increasing toxicity; Mg an d K were negatively correlated with increasing toxicity. Toxicity test s with SnCl2 revealed that the toxicity threshold for Sn was far above the concentrations present in the raw effluent. Reduction of Ca was s hown to result in a significant improvement in survival, but some toxi city still remained. Further augmentation of the treated effluent with CaCl2, MgCl2, and KBr to restore the concentrations of Ca, Mg, K, and Br to natural seawater concentrations resulted in survival of all exp osed organisms. Repeated success of this treatment regime on additiona l samples of the effluent as well as ''mock effluent'' studies confirm ed that ion imbalance was the sole source of toxicity in this effluent . Process source water composition and essential ion balance are discu ssed as important components of marine effluent TIEs.