Tonto Creek Fish Advisory Risk Analysis 7-11
Total Page：16
File Type：pdf, Size：1020Kb
Fish Consumption Risk Analysis for Tonto Creek, Arizona July 2011 BACKGROUND INFORMATION boundary at Gisela, the creek flows into the valley Tonto Creek is a perennial stream located in Gila between the Mazatzal and Sierra Ancha mountains County, in central Arizona. From its origin at Tonto ending at an altitude of 2,119 feet where it flows Springs, just below the Mogollon Rim, Tonto Creek into Roosevelt Lake. flows through dense Ponderosa pine forest, deep Geology canyons and desert chaparral to its confluence with Tonto Creek Spring issues from a limestone the Salt River at Roosevelt Lake (Figure 1). Along its aquifer in an area of Permian to Pennsylvanian sed- course, it receives the flows of several smaller imentary material and then flows through streams including Horton, Spring, Christopher and Mississippian, Devonian, and Cambrian sedimenta- Haigler Creeks and runs past summer cabins in the ry rocks. As it flows through the canyon of the Kohl’s Ranch area and Bear Flats and through the Hellsgate Wilderness it meets Early Proterozoic rural areas known as Gisela, Punkin Center and quartzite, granitic and metavolcanic rocks. Below Tonto Basin. the wilderness at Gisela, Tonto Creek runs through At 72.5 miles in length, Tonto Creek is a Strahler Pliocene to middle Miocene deposits and early fifth order stream and has a 955 sq. mi. watershed Pleistocene to latest Pliocene surficial deposits. at the confluence with the Salt River. Starting just Within the Tonto basin, there are several occur- below the Mogollon Rim at an altitude of 7,400 rences of barite (barium sulfate), a mineral that feet, the creek then descends through a steep often co-occurs with cinnabar (mercuric sulfide), as canyon, in places almost 1,000 feet deep within the well as mineable quantities of cinnabar itself. Hellsgate Wilderness. At the lower wilderness Publication Number: OFR 11-05 1 Figure 1. Tonto Creek, Arizona 2 SAMPLING, STANDARDS AND ANALYSIS piscivorous fish. No fish other than rainbow trout, Mercury speciation and analysis brown trout and desert suckers were found. Results All fish tissue samples referenced in this report are summarized in Table 1 and Figure 2 below. were analyzed for, and the results reported as, total In the Bear Flats area south of Camp Tontozona mercury (THg). The total mercury data was then the 11 rainbow trout taken had a mean Hg con- used as a surrogate for methylmercury in the risk centration of 0.2 mg/Kg with a range of 0.02 to 0.3 analysis. While methylmercury is generally consid- mg/Kg. Six brown trout had a mean concentration ered the more toxic fraction in consumable fish of 0.2 mg/Kg with a range of 0.1 to 0.3 mg/Kg. Four tissue, total mercury and methylmercury in fish desert suckers had a mean Hg concentration of 0.6 tissue are well correlated (Bloom, N.S. 1992, mg/Kg with a range of 0.4 to 0.7 mg/Kg. Maršálek et al. 2006, Kuwabara et al. 2007, Storelli From Tonto Narrows to Roosevelt Lake the 17 et al. 2003, Lasorsa and Allen-Gil 1995) with smallmouth bass taken had a mean tissue Hg con- methylmercury comprising ~95-99 percent of the centration of 1.5 mg/Kg with a range of 0.4 to 3.0 total mercury analyzed. Total mercury analysis is mg/Kg. 13 common carp had a mean Hg concen- also less complex, less expensive and allows long tration of 0.5 mg/Kg with a range of 0.3 to 0.8 term comparison with national and State data sets. mg/Kg. Four green sunfish had a mean Hg concen- These data sets are influenced by the condition tration of 1.0 mg/Kg with a range of 0.6 to 1.4 (relative weight (Wr) or “fatness”) of the fish. mg/Kg. Three black bullhead catfish had a mean concentration of 1.1 mg/Kg with a range of 0.6 to Sampling 1.9 mg/Kg. A single largemouth bass and a single In 2002, the U.S. Environmental Protection desert sucker had Hg concentrations of 0.4 and 0.6 Agency (USEPA) sampled fish from Tonto Creek just mg/Kg respectively. below the Hellsgate Wilderness Area as a part of the Regional Environmental Monitoring and Assessment Standards Program (REMAP). Five fish were taken without In the last surface water quality standards rule- recording species and categorized as either small or making approved January 2009, the State adopted large. The mean mercury concentration for all fish a fish tissue standard of 0.3 mg/Kg for methylmer- from this sample was 1.11 mg/Kg with a range of cury for protection of the fish consumption desig- 0.652 to 2.275 milligrams per kilogram (mg/Kg) nated use. This fish tissue standard was used in cal- (N=5). Due to flooding in Tonto Creek, fish were culating the lower safe limit in this advisory. The not again sampled until 2006. consumption advice contained in this document is Currently, the Arizona Department of based on a risk analysis derived using the USEPA Environmental Quality (ADEQ) and the Arizona reference dose for methylmercury (USEPA, 2002). Game and Fish Department (AGFD) work coopera- RISK ANALYSIS tively in the collection of fish for the fish consump- In aquatic ecosystems with a conducive water tion advisory program. Since 2006 fish in Tonto chemistry, (the right balance of sulfate, dissolved Creek were sampled on five occasions along three organic carbon, a favorable redox potential and sections of the creek by ADEQ and AGFD. A total bacteria population), methylation; which is the of eight different species were taken: smallmouth incorporation of mercury into an organic molecule, bass (Micropterus dolomieu), common carp takes place at a rapid rate. Once methylated, mer- (Cyprinus carpio), green sunfish (Lepomis cyanellus), cury moves through and up the food web quickly black bullhead catfish (Ameiurus melas), desert and becomes concentrated in high order predators sucker (Catostomus clarki) and largemouth bass such as largemouth or striped bass, northern pike (Micropterus salmoides) were taken in the section and/or walleye. Upon ingestion by humans, from Tonto Narrows upstream of Gisela to methylmercury is readily absorbed through the gas- Roosevelt Lake. Rainbow trout (Oncorhynchus trointestinal tract and easily penetrates the blood- mykiss), desert sucker and one brown trout (Salmo brain and placental barriers. While methylmercury trutta) were taken in the area of Bear Flats just has been linked to a variety of health effects, the upstream of the wilderness boundary. An extensive primary risk arises from its toxicity to the nervous survey for piscivorous fish was conducted in the system, including the brain. Most at risk are infants Bear Flats and Camp Tontozona portions of Tonto and unborn children whose mothers consume fish Creek to determine the presence or absence of containing methylmercury during pregnancy or 3 while nursing. Chronic exposure to methylmercury may cause gross cranial defects, cerebral palsy and at elevated concentrations can cause developmental a decrease in living fetuses. delays and learning disabilities, and acute exposures Table 1. Mercury in fish filet tissue from Tonto Creek, Arizona 4 Figure 2. Mercury in fish filet tissue from Tonto Creek, Arizona TOXICOLOGY AND REFERENCE DOSE An RfD is an estimate of a daily oral exposure that is likely to be without any appreciable risk of adverse health effects. For determining safe rates of consumption, the EPA RfD of 0.0001 mg/Kg-day is used. This RfD is based on a study of women and children who episodically ate methylmercury tainted fish and pilot whale meat in the Faroe Islands and considers impairment of chil- dren’s neurological function that cause developmental Methylmercury is considered a Class C (possible) delays. Mean body weights for all age/sex classifica- human carcinogen due to increased incidence of tions are calculated using data from the National renal adenomas, adenocarcinomas and carcinomas Health and Nutrition Examination Survey observed in male mice. These effects were found in (NHANES) (Portier, et al., 2007). Total mercury the presence of profound nephrotoxicity caused by concentrations used in the risk calculation are the exposure to the toxicant and may be a conse- means for the individual species. quence of reparative changes in the cells. While methylmercury may not be a strong mutagen, it has POSSIBILITY OF ACUTE TOXICITY been shown to induce chromosomal aberrations. While developmental chronic toxicity is the Neurologic effects include erythism or “mad hatter major concern when considering mercury, it is also syndrome”, tremors, paresthesia, slowed brain important to address the possibility of acute toxicity. activity, memory disturbance and sleep disorders. Biokinetic modeling (Ginsberg and Toal, 2000) has (USEPA, 2002) predicted the elevation of certain biomarkers asso- ciated with neurodevelopmental effects as a result CALCULATION OF RISK FOR CHRONIC EXPOSURE of the consumption, during pregnancy, of a single While Arizona has a standard for methylmercury eight ounce fish meal at or above 2 mg/Kg in fish tissue, fish containing mercury can still be methylmercury. Using this concentration as a deci- part of a healthy diet if consumed at a rate that will sion making tool will allow an analysis of possible not cause mercury to accumulate to toxic concen- acute effects that may occur if a much larger than trations in the human body. To determine this rate, average fish were caught and consumed. Because the following formula is used: tissue mercury concentrations often correlate well with length and/or weight within a single fish species (Gewurtz, S. et al. 2011), ADEQ may be able to predict Hg concentrations in fish larger than those taken for analysis by correlating length with Hg and extrapolating out to State record length.