Elimination of Whole Effluent Toxicity NPDES Permit Limits through the Use of an Alternative Testing Species and Reasonable Potential Analysis Page: 3 of 8
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ALTERNATE SPECIES DEVELOPMENT
C. dubia is the predominant species used by the Environmental Protection
Agency (EPA) for WET testing because it has been researched so extensively.
It is easy to culture in the laboratory, making it amenable for
.a_ use across the United States. However, it is not the only
species that can provide adequate performance when
determining toxicity in effluent discharges. D. ambigua was 4'
chosen by WSRC as a possible alternate testing species
because it is commonly found in fresh waters of the C. dubia
southeastern United States. According to the literature, it is
D. ambigua fairly easy to culture in the laboratory. Most importantly, it can thrive in soft
waters such as those found at SRS, making it a better species to use when
determining toxic affects from effluents discharged into streams with low hardness.
Gaining regulatory approval to use D. ambigua in WSRC WET compliance tests required side-
by-side testing against C. dubia. Research was conducted by personnel from WSRC and the
University of South Carolina in which both species were cultured and tested for sensitivity to
specific toxicants as well as to local surface waters. Results indicated that D. ambigua is a good
replacement for C. dubia in soft waters and in streams that have naturally low pH values.
Sensitivities between the two species were comparable. Full-scale tests using soft water from
local streams resulted in reproduction problems in C. dubia, but seemed to enhance reproduction
in D. ambigua. Study results were transmitted to SCDHEC and EPA-4 with a request to allow
WSRC to use the alternate species in WET compliance tests.
EPA-4 and SCDHEC reviewed all data and, after a very careful and lengthy deliberation period,
provided approval for WSRC to use D. ambigua instead of C. dubia in WET compliance tests.
The approval process lasted over two years from start to finish, beginning with SCDHEC and
ending with EPA-4. Additional data was provided to EPA-4 at their request during the two year
period. Final approval was provided by EPA-4 only when the toxicologist at their Ecosystems
Research Division in Athens, Georgia, was in agreement with all research data and conclusions.
The approval from EPA-4 was for D. ambigua only. This meant that WSRC could not use C.
dubia in the event that problems arose while testing with D. ambigua. WSRC objected at first,
but after healthy cultures of D. ambigua were generated quickly and WET testing was successful
for several weeks, WSRC dropped their objection.
Even though EPA-4 did not approve the use of both species for compliance tests, tests were
performed using both species initially just in case problems developed with D. ambigua. D.
ambigua had been cultured and used only for the purpose of obtaining regulatory approval. It had
not been used in actual compliance testing and there were unknowns regarding how consistently
it would perform. The contract lab was asked to run side-by-side WET tests with both species
using the exact same protocols that were required for compliance testing. The success rate was so
high with D. ambigua that tests using C. dubia were eventually eliminated (Table 1).
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PAYNE, W.L. Elimination of Whole Effluent Toxicity NPDES Permit Limits through the Use of an Alternative Testing Species and Reasonable Potential Analysis, article, May 24, 2004; South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc788701/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.