Use of existing water, sediment, and tissue data to screen ecological risks to the endangered Rio Grande silvery minnow.
A screening-level ecological risk assessment was applied to two extensive, but previously unanalyzed datasets from the middle Rio Grande (MRG) in New Mexico. The assessment evaluated how adverse water-quality effects from aquatic toxicants may have influenced the population decline of the endangered Rio Grande silvery minnow (Hybognathus amarus; silvery minnow). Standardized US Environmental Protection Agency (USEPA) screening-level ecological risk assessment procedures were applied to chemicals assessed in samples collected from the MRG between 1985 and 2003. Since more chemicals have established risk-screening criteria, relative to water-quality criteria, this approach produces more complete assessments. Chemical concentrations at some locations and times were potentially sufficient to affect fish health or produce localized mortalities. Many constituents displaying the highest risks have substantial natural sources within the watershed; native species likely would have adapted to natural instream concentrations such that actual risks might be markedly less than projected by a risk screening based on generic aquatic-life criteria. Also, highest risks found for individual and combinations of contaminants were very inconsistent both within and across the sites. As such, this risk assessment does not support the conclusion that toxicants were a primary factor causing the silvery minnow population to decline in the MRG between 1985 and 2003. The assessment indicates that sediment-borne, relative to water-borne, contaminants appeared to present the greatest risks to the silvery minnow and thus should have increased focus during future assessments of potential contaminant effects in the MRG. Contaminants of greatest concern are identified. This study presents approaches to cost-effectively assess and reduce uncertainties associated with potential water quality effects, and to help direct future assessments of water quality onto those contaminants likely to produce potentially significant effects. The techniques presented and criteria compiled are suitable for aiding similar assessments in other aquatic habitats.
Marcus
Michael D
MD
Tetra Tech, Inc. 6121 Indian School Road NE, Suite 205, Albuquerque, NM 87110, United States. mike.marcus@tetratech.com
Covington
Sean
S
Liu
Beiling
B
Smith
Natalie R
NR
D000818:Animals; D003530:Cyprinidae / Q000378:metabolism*; D056727:Endangered Species; D004784:Environmental Monitoring / Q000379:methods*; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D009516:New Mexico; D018570:Risk Assessment; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000592:standards; D014877:Water Pollution, Chemical / Q000706:statistics & numerical data
D014874:Water Pollutants, Chemical