Freeze concentration of ambient waters for toxicity testing

We have developed a method to concentrate aqueous samples for toxicity testing. This method relies on the phenomenon of freezing exclusion, whereby solutes are rejected from the interstices of a growing ice crystal. Tenfold freeze concentration gave excellent recoveries of inorganic and organic analytes, phenol and ZnSO4 toxicity from spiked natural waters, and toxicity of both pre- and postdischarge municipal wastewater. Simultaneous 10-fold concentration of strong mineral or humic ambient matrices did not substantially modify the expressed toxicity of phenol or ZnSO4, and it did not seem to generate spurious toxicity to the marine bioassay organism used (Vibrio fischeri). Hundredfold freeze concentration permitted the quantification of low levels of ambient toxicity in a wide variety of natural waters using a rapid, inexpensive microbioassay. Precipitation of matrix elements may limit the degree of concentration that can be achieved with highly mineralized or strongly humic waters. This approach is well suited to ambient toxicity testing, because it is nonspecific and has low potential for solvent contamination. Furthermore, the low temperatures involved minimize volatilization and degradation of organic contaminants.