Discharge limits for specific toxicants are based on water
quality standards. Most states
promulgate water quality standards based on national water quality criteria
issued by EPA. The national criteria are
calculated from databases consisting of numerous toxicity tests performed on a
variety of species and life stages.
These tests are generally performed using a spiked laboratory dilution
water consisting of filtered well or tap water or “synthetic” fresh or salt
water (deionized water plus essential salts). However, a variety of physical and chemical characteristics of natural
surface waters (e.g. dissolved organic carbon, pH, hardness, suspended solids)
may affect toxicity. For example, the toxicity of many metals in stream water
is often much less than the toxicity predicted from the EPA criterion or state
standard. Each stream is different depending on the drainage basin, geology, etc.
A site-specific water quality standard can be derived
generating sufficient toxicity data using site water and a variety of
species representing different taxonomic groups. However, this approach
expensive because of the amount of data that must be generated and the
difficulties often encountered in testing non-standard organisms.
Another, more economical, approach is to perform
side-by-side toxicity tests in both laboratory dilution water and
water using standard species. The
calculated water-effects ratio (WER) is then
used as a multiplier to correct the national or state standard for
site-specific conditions. Further
modifications to the standard may also be made by accounting for
differences in water chemistry (e.g. dissolved-to-total ratio and
hardness for metals) between the site water and regulatory default
Coastal Bioanalysts, Inc. can provide the technical
necessary to derive a site-specific water quality standard. We are
experienced with a wide variety of
test species and can perform toxicity tests using methods (e.g.
static renewal) appropriate for the toxicant and site-specific
conditions. We have conducted numerous WER studies, providing clients
with cost-effective regulatory relief.