Critical examination of the data generated during the toxicity identification evaluation (TIE) programs showed that to be confident in isolating the responsible toxicants present in the effluent, a large number of samples have to be collected and fractionated, since a wastewater sample may be representative only of the discharge at the time of sampling. Changes in effluent toxicity can result from varying concentrations of individual toxicants or different toxicants, due to changes in plant operation and/or changes in source water quality characteristics. Source water may be toxic by itself or may affect the toxicity of wastewater constituents. Understanding the contribution of background sources to effluent toxicity including the nature, frequency, concentration in use, and relative toxicity of additives introduced during industrial processes is important in the TIE investigation.
In the case reported, site inspections identified four primary sources (brook water, industrial water, well water and town water) of noncontact and cooling process water which supported plant operations. Variability studies conducted on each influent source included 48-h static acute toxicity tests with Daphnia pulex and chemical analyses. The results of the source water characterization indicated that the brook water was not acutely toxic, the industrial water was periodically toxic, typically at mid-week, and the toxicity observed was inconsistent. A moderately toxic sample (mean 48-h LC50 of 64%) was followed by a more toxic sample (mean 48-h LC50 of 10%) the following week. During this time the suspected toxicant present shifted from copper to total residual chlorine in the industrial water source. Well water was moderately toxic due to volatile organics and town water was highly toxic due to copper. The four influents are used in various amounts for the specific manufacturing operations and are the main component of ten individual effluents which are discharged to the receiving water. Toxicity reduction strategies for these wastewaters were complicated by the presence of toxicity in water sources uncontrolled by industrial users.