Assessment Comments
Assessment remains based on results of U.S. EPA/IDNR fish contaminant monitoring conducted in 2001 for U.S. EPA's "National Lake Fish Tissue Study."
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. Fish consumption uses are assessed (evaluated) as "partially supported" based on results of fish contaminant monitoring conducted in August 2001 for U.S. EPA’s National Lake Fish Tissue Study.
EXPLANATION: The Class B(LW) aquatic life uses remain "not assessed" due to the lack of water quality information upon which to base an assessment.
Fish consumption uses are assessed (evaluated) as “partially supported” based on results of the U.S.EPA/IDNR fish contaminant monitoring conducted as part of EPA's National Lake Fish Tissue Study in 2001. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa. In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol. This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol). Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest impairment of the fish consumption uses.
Although this scenario does not apply to the fish contaminant data generated from the 2001 sampling conducted at Percival Lake, levels of contaminant are sufficiently high for concern and justify follow-up monitoring. The levels of at least one contaminant from past monitoring now exceeds one or more advisory trigger levels, thus suggesting the need for additional (follow-up) monitoring to determine whether a consumption advisory should be issued.
The composite samples of whole-fish common carp and largemouth bass fillets had generally low levels of contaminants. Levels of primary contaminants in the composite sample of common carp were as follows: mercury: 0.106 ppm; total PCBs: < detection. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.313 ppm; total PCBs: < detection. Although assessed as “fully supported” for this reporting cycle, the level of at least one contaminant does, however, now exceed one or more advisory trigger levels: the level of mercury in the sample of largemouth bass fillets (0.313 ppm) exceeds the one meal per week trigger level of 0.20 ppm.
According to the IDNR/IDPH advisory protocol, this single result from the 2001 sampling at Percival Lake does not warrant issuance of a consumption advisory: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. But, this elevated level does indicate a potential impairment and the need to conduct additional monitoring to better define contaminant levels in fish from this waterbody. Thus, the fish consumption uses are assessed as “partially supported”. Because the impairment is poorly defined and not confirmed, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Follow-up monitoring will be conducted in 2007 to better determine levels of mercury in the edible portions (fillets) of fish in Percival Lake and to determine whether a one-meal-per-week consumption advisory needs to be issued.
