HEALTH CONSULTATION
Public Comment Release
FISH SAMPLING IN PUTAH CREEK (PHASE II)
LABORATORY FOR ENERGY RELATED HEALTH RESEARCH
DAVIS, YOLO COUNTY, CALIFORNIA
The purpose of this health consultation is to report the results from an ATSDR fish survey of the fish in Putah Creek in 1997, and report our conclusions and public health recommendations from that survey. The survey was conducted to better define the concentrations of mercury and lead in different fish species in Putah Creek.
This report is the second health consultation issued by the Agency for Toxic Substances and Disease Registry (ATSDR) which addresses fish in Putah Creek near the Laboratory for Energy-Related Health Research (LEHR) Superfund site on the University of California at Davis (UCD) campus, in Davis, California.
ATSDR recommended in a Site Summary report in December 1995 that fish in Putah Creek should be sampled and analyzed for hazardous substances, because people were eating fish from Putah Creek and there had been no previous analyses of the fish [1]. The U.S. Environmental Protection Agency (EPA) Region IX collected fish and crayfish, water, and sediment samples from four locations along the creek, and the EPA National Air and Radiation Environmental Laboratory (NAREL) analyzed the samples for ATSDR. ATSDR released a health consultation in April 1997 describing the results of the first fish survey [2].
The most important conclusion in the first health consultation was that mercury and lead concentrations in some fish collected from Putah Creek pose a public health hazard to people who eat the fish. However, NAREL composited many of the fish and crayfish before analyzing them because the laboratory required certain sample volumes to do all the analyses planned (18 pesticides and other organic chemicals, 14 metals, gross alpha, gross beta, and gamma spectrometry). Compositing the fish was appropriate for an initial screening survey of this kind.
Because mercury and lead were elevated in composite fish samples, ATSDR recommended in the first health consultation that an additional fish study be conducted to better define the concentrations of mercury and lead in different fish species. EPA agreed to assist ATSDR again, to collect a second round of fish and crayfish from Putah Creek. This health consultation reports the results of those efforts.
EPA Region IX collected a total of 152 fish and crayfish, plus water and sediment samples, at five locations along Putah Creek in October and November 1997. EPA staff were assisted by staff from Thomas R. Payne & Associates, Inc. (TRPA). TRPA is an independent contractor conducting fisheries monitoring on lower Putah Creek for the Solano County Water Agency. TRPA has sampled fish in Putah Creek for six years. Their staff shared their fishing expertise and their knowledge of Putah Creek with EPA staff for this ATSDR program. EPA Region IX scientists packaged the samples and sent them to the NAREL in Montgomery, Alabama, for analysis. NAREL scientists homogenized the whole fish or crayfish. Composite samples of two or more fish were prepared of some of the fish, of a single species and size range from a single location.
We have attached the data from the laboratory analyses of fish, water, and sediment collected from Putah Creek to the end of this report. ATSDR scientists and NAREL scientists reviewed the NAREL data. ATSDR offers the following results, conclusions, recommendations, and follow-up public health actions based on these data.
Women of child bearing age, especially those who are pregnant or are nursing, should refrain from eating largemouth bass from Putah Creek.
FOLLOW-UP PUBLIC HEALTH ACTIONS
Although we were able to catch a substantial number of bluegill and we had enough fish of each species to adequately complete our laboratory analyses, we had important gaps in some fish species and fish sizes that limit what we can state about the hazards from eating these fish. The low numbers of channel catfish, carp, and black bullhead we collected mean that we have less certainty that the concentrations of metals and radionuclides we measured are typical of the concentrations we would find throughout these species in Putah Creek. In addition, the numbers of fish of different species that we caught may not be representative of what local fishers typically catch and eat. For example, we collected only one channel catfish. However, catfish are a species sought by fishers, and people who fish from Putah Creek likely catch and eat more of these fish than our data suggest.
Largemouth bass:
Mercury was detected in all the largemouth bass that we caught. The large-sized largemouth bass have more mercury and higher concentrations of mercury in them than the small-sized largemouth bass; thus, the largemouth bass are bioaccumulating mercury. As a first approximation, mercury concentration increases in largemouth bass by one unit (1 mg/kg-fish) for every two kilograms increase in body mass of the fish. See Figure 1. We have also plotted milligrams of mercury vs. fish mass for largemouth bass in Figure 2 to show how mercury content increases with (largemouth bass) fish size.
There is no indication that the location where we caught largemouth bass had any significant bearing on the accumulation of mercury. When we take into consideration the size of the fish, mercury accumulation in largemouth bass was consistent at all locations where we caught those fish. However, we only caught large-sized largemouth bass at locations 1 and 2, and no largemouth bass at location 4. We would have liked to have caught fish from each size range at each location to better determine whether location had any affect on mercury accumulation. We suspect, however, that these data gaps are not important because the fish do not stay at one location and mercury concentrations in sediment were similar at all locations (0.7 ± 0.4 mg mercury per kilogram sediment dry weight). Therefore, until more or better data become available, we expect that other largemouth bass caught in this area of Putah Creek will contain mercury at concentrations similar to those we found in this survey.
ATSDR has proposed a minimum risk level (MRL) for chronic oral exposure to methylmercury of 0.0005 milligrams of methylmercury per kilogram body weight per day (0.0005 mg/kg/day) [3]. An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without an appreciable risk of adverse noncancerous health effects over a specified duration of exposure. ATSDR derived this proposed MRL primarily from a study designed to test the hypothesis that prenatal exposure to low concentrations of methylmercury through maternal ingestion of fish is related to child development outcomes [4]. The child development outcome that was noted in the study that apparently arose from the lowest exposure levels of mercury that were above the proposed MRL is decreased physical activity in male infants.
We have assumed that all the mercury in the fish we caught in Putah Creek is methylmercury. We considered, as we did in our previous health consultation, an average consumption rate of 54 grams of fish per day [5]. This amount (54 grams = 1.9 ounces) is an average daily rate derived from an equivalent of approximately two meals of fish per week (e.g., 1.9 ounces/day x 7 days = 13.3 ounces per week). For a 60 kilogram adult female eating 54 grams of fish per day, the proposed MRL equates to approximately 0.56 mg/kg-fish, or 0.56 ppm in fish. We used 0.56 mg/kg-fish as our screening value for mercury in fish. Mercury concentrations in the two largest largemouth bass exceeded this value.
The concentrations of mercury we observed in the two largest largemouth bass could have an effect on the development of the fetus or the nursing child whose mother eats these fish more than once a week. We acknowledge that a typical fish meal from Putah Creek will likely contain fish other than largemouth bass, and mercury levels in the majority of the largemouth bass caught in this survey are below the ATSDR proposed MRL. However, Putah Creek may also contain larger largemouth bass than the ones we caught, and we expect larger largemouth bass will have higher levels of mercury than those we measured(1). Therefore, we recommend that pregnant and nursing women avoid eating largemouth bass from Putah Creek because of the possibility they will eat larger fish than those we caught, as well as the uncertainties in the consumption rates of women eating fish from Putah Creek.
Crayfish:
Crayfish contained the highest levels of lead we measured in this fish survey. Lead was detected in all the crayfish samples.
Lead is a toxic metal that affects virtually every system in the body. It is particularly toxic to developing fetuses and young children. Developmental neurobehavior effects have been observed in humans following prenatal exposure to low levels of lead [7]. In 1991, the Centers for Disease Control (CDC) recommended a threshold for intervention of 10 micrograms of lead per deciliter of blood (10 µg/dL) in children [8]. We evaluated lead in fish by considering whether the concentrations of lead in the crayfish could lead to blood lead levels of 10 µg/dL.
We used a consumption rate of 54 grams of crayfish per day and a diet slope factor of 0.034 µg/dL per µg of lead ingested per day to calculate the blood lead level of a pregnant woman eating crayfish at the highest concentration of lead in crayfish that we measured [5,9].
We considered that people may eat more crayfish (total mass) per meal than they eat of finfish, but they eat fewer meals of crayfish per month (on average) than meals of finfish. There are few fish consumption surveys available that estimate shellfish consumption separate from total fish consumption. It appears that the consumption of shellfish among fishers and their families may be half, or less, than that of finfish [10]. For our calculations, and to be conservative, we used the same consumption rate (54 grams per day) as we used for finfish.
Our calculations indicate the blood lead level of a woman eating crayfish with the maximum levels of lead we measured would be approximately 2 µg/dL. Inhalation of dust and consumption of other food and beverages will contribute an additional 0.5 µg lead per dL blood [7]. The combined blood lead concentration (2.5 µg/dL) from crayfish and other environmental sources is well below the threshold for intervention (10 µg/dL) for blood lead levels in children. Therefore, the lead levels in the fish we collected from Putah Creek are not a public health hazard to fetuses or infants whose mothers eat those fish.
In addition to the fish, EPA staff collected water and sediment samples at the five fishing locations along Putah Creek. None of the concentrations of metals or radionuclides detected in water or sediment samples were at levels of health concern. The only radionuclides detected in these samples that are not naturally occurring are cesium-134, cesium-137, and iodine-131. Iodine-131 was detected in water and the cesium isotopes were detected in sediment. Neither iodine nor cesium were detected in fish(2). The concentrations of metals and radionuclides in sediment were similar at all five locations. We are providing those data at the end of this report along with the fish data.
This health consultation does not address whether some fish in Putah Creek may be safe to eat. We did not collect a sufficient quantity of some fish species (e.g., black bullhead, channel catfish) to know whether the contaminant levels we measured in these fish are representative of the concentrations in their respective populations in Putah Creek. In addition, we have only incomplete data describing concentrations of toxic organic substances, such as pesticides, in the fish in Putah Creek. (The NAREL laboratories did not analyze any of the fish collected in this survey for toxic organic substances.) None of the information we do have-- except mercury in largemouth bass as described in this report-- indicates the fish in Putah Creek pose a health hazard to people who eat them. However, the data we have do not fully address whether toxic organic substances are at levels of health concern in the fish.
We have found, after two surveys, that it is not a simple matter to collect sufficient numbers of fish of different species to perform all the laboratory analyses we need to reach conclusions and make public health recommendations. This suggests that we may not be able to catch enough fish to answer all the questions about the safety of the fish as a food source that we would like to have answered. An alternate approach, such as conducting a more thorough survey of creek sediment, or surveying an indicator species, such as freshwater clams (Corbicula fluminea) may provide more useful information. ATSDR is currently evaluating the information that is available. We welcome any comments and suggestions and will evaluate these fully before recommending further investigations of Putah Creek.
Figure 1. Mercury in Largemouth Bass
Figure 2. Mercury in Largemouth Bass
William H. Taylor, PhD, DABT
Health Assessor
Federal Facilities Assessment Branch
ATSDR
Burt J. Cooper
Chief, Energy Section
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
ATSDR
ATSDR acknowledges and thanks Thomas Payne and Associates, Inc., California Department of Health Services-Environmental Health Investigations Branch, EPA Region IX, and EPA NAREL for assistance with this project.
The preparer of this report also acknowledges and thanks the following ATSDR staff who provided their assistance and expertise: Henry Abadin, M.S.P.H.; Richard Canady, PhD; Gwendolyn Eng; Richard (Mike) Fay, PhD; Beverly Harris; Theresa NeSmith; John Risher, PhD; Allan Susten, PhD.
For further information, or to request copies of our documents, including Toxicological Profiles and Case Studies in Environmental Medicine, contact ATSDR on our toll-free number: 1-800-447-1544, or visit our Internet Home Page at http://www.atsdr.cdc.gov/.
Next Section Table
of Contents
