Finalized June 2015 Technical Report: Soft-shell clam advisory for the Oregon coast Summary The Oregon Department of Environmental Quality (DEQ) recently completed analysis of contaminants in the tissue of shellfish collected at multiple sites along the Oregon coast. During 2013 limited samples of softshell clams (Mya arenaria), purple varnish clams (Nuttallia obscurata) and Olympia oysters (Ostrea lurida) were collected from several locations in bays and estuaries. The tissues were analyzed for a suite of potential environmental contaminants including metals (arsenic, mercury, cadmium, selenium), chlorinated pesticides, polychlorinated biphenyls, polybrominated diphenyl ethers, dioxins, furans, and organic tin compounds. The US Environmental Protection Agency (EPA) has identified screening levels for these contaminants as the daily human doses of hazardous substances that are not likely to cause adverse health effects. Most contaminants were below the EPA screening levels for the target analytes monitored by the Oregon Health Authority / Fish Advisory Program. The DEQ analysis (2013-2015), however, revealed that inorganic arsenic concentrations were above the fish advisory screening level of 0.7 mg/kg tissue at several locations along the Oregon coast for whole bodies of the softshell clam. The analysis also indicates that the level of inorganic arsenic only exceeded the screening level in softshell clams when the siphon sheaths were intact. The levels of inorganic arsenic were well below the screening level when the siphon sheaths were removed from the softshell clams. No other species of shellfish exceeded the screening level for inorganic arsenic. Average inorganic arsenic concentrations did not come within an order of magnitude of the screening value in any species other than softshell clams. Based on these data, the Oregon Health Authority / Public Health Division (OHA) developed a human consumption advisory for softshell clams along the Oregon coast. Meal recommendations vary between 1-4 meals per month for whole clams with intact siphon sheaths, and between 11-33 meals per month for clams from which the siphon sheaths have been removed. Clam diggers should be advised to properly prepare softshell clams by removing the siphon sheath prior to consumption. This technical report describes methodology followed by OHA to develop a human consumption advisory for softshell clams (Mya arenaria) along the Oregon coast. The background section describes the Oregon coast, the approximate numbers of Oregonians that harvest and consume shellfish collected locally along the coast, and environmental sampling that provides the foundation for the consumption advisory. The assessment section provides a summary of the sampling effort and levels of inorganic arsenic measured in softshell clams and OHA’s evaluation of the data and derivation of the recommended meal limits. The results section summarizes the recommendations regarding meal consumption, and the discussion section describes next steps and practical implications. The limitation section acknowledges continuing areas of scientific uncertainty. Background Description of water body and use of its shellfish resources Oregon’s western border terminates in the Pacific Ocean and encompasses about 363 miles of coastline. Oregon’s coastline provides habitat for many species of marine and estuarine shellfish, and many Oregonians collect and consume these shellfish. Different species of shellfish occur along the open coast and in the lower and upper regions of bays and estuaries. The Oregon Department of Fish and Wildlife (ODFW) issues approximately 180,000 licenses for recreational shellfish harvest per year statewide. 1 Finalized June 2015 ODFW developed estimates of the annual number of clam digger trips for four of the most popular bays visited by recreational clammers over the period from 2008 to 2012 (Table 1). These estimates range from about 8,500 trips per year at Tillamook Bay to about 14,000 trips per year at Netarts Bay. Most of these recreational clam digger trips are focused on collection of several popular species of “bay clams” including gaper clams, cockles, butter clams, and littleneck clams. In addition, sport harvesters also target other popular species such as razor clams, purple varnish clams, mussels, and crab (Dungeness crab and red rock crab). ODFW estimates that a very small fraction (likely less than 0.1%) of the recreational clam digger trips are focused on harvesting softshell clams (Mya arenaria). California mussels (Mytilus californianus) harvesting occurs coast wide. Harvest of native Olympia oysters (Ostrea lurida) is prohibited in Oregon. Among the popular species of targeted clams, only softshell clams and gaper clams have a tough leathery sheath covering their siphons. Environmental monitoring of shellfish resources In summer of 2013, DEQ partnered with ODFW and ODA to collect 20 composite samples of bivalve shellfish from different locations along the Oregon coast. Preliminary results generated by the statewide sampling effort became available to OHA in early March 2015. This assessment was carried out as a component of the DEQ Toxics Monitoring Program. The DEQ Statewide Toxics Monitoring Program was initiated in 2008 following authorization of funding by the Oregon Legislature in 2007. The goals of the DEQ Toxics Monitoring Program are to: • Gather information to characterize the presence and concentration of chemicals of concern in Oregon’s waters; • Use this information to identify sources of these chemicals; • Present and make available information gathered for public benefit; and • Work with DEQ internal groups, community groups and Oregon citizens to identify opportunities for reducing these pollutants. In this case, sample locations and species sampled were chosen to evaluate the presence of contaminants in shellfish along Oregon’s coast from an ecological point of view. Two species (softshell clams and California mussels) that live along the entire coast were chosen for data comparison between sites without regard to differences in feeding, habitat, and life cycle. Arsenic is a trace metal and chemical element that occurs naturally in sediments, bedrock, groundwater, plants, and animals. Inorganic arsenic is the toxic form of arsenic. This form is often associated with natural geology and rock formations but can also be introduced into the environment from pressuretreated wood, outdoor building materials, and by agriculture and industrial activities. Oregon’s geology is naturally high in arsenic, and it is difficult to definitively identify the specific source of arsenic in the environment and in shellfish. 2 Finalized June 2015 Table 1. Estimated number of recreational clam digger trips each year to Tillamook, Netarts, Yaquina, and Coos Bays (from ODFW / Shellfish Program) Bay Tillamook Bay Netarts Bay Yaquina Bay Coos Bay Year Total Clam Digger Trips (#/yr) 2008 9,832 2009 9,218 2010 6,207 2011 6,134 2012 11,018 2008 12,081 2009 23,262 2010 11,117 2011 9,786 2012 13,653 2008 6,114 2009 13,002 2010 11,961 2011 7,363 2012 7,052 2008 13,598 2009 15,428 2010 13,030 2011 11,113 2012 9,729 3 Finalized June 2015 DEQ analyzed the shellfish tissue for multiple analytes. During review of the data particular concern was raised about the levels of arsenic detected in the samples. DEQ has recently developed methods to speciate total arsenic into inorganic and organic fractions. DEQ used these methods on shellfish tissue collected in 2013. The distinction between organic and inorganic arsenic is important because in most finfish and other common seafood, the majority of the total arsenic in tissue (90% or more) is made up of organic arsenic compounds that are virtually non-toxic. Only the inorganic fraction of arsenic is toxic. The DEQ analysis revealed that inorganic arsenic made up only 1-6% of the total arsenic in the samples of oysters, mussels, and purple varnish clams. In contrast, inorganic arsenic made up 50-100% of the total arsenic in softshell clams (Mya arenaria). Using the 2013 dataset, it was determined that inorganic arsenic concentrations were above OHA’s fish advisory screening value at several locations along the Oregon coast for Mya arenaria. Because inorganic arsenic proportions were higher than expected in softshell clams, an interagency group including OHA, DEQ, ODA, and ODFW decided to collect and analyze an additional set of softshell clams to: (1) determine if the data from 2013 could be replicated; and (2) determine whether proper preparation and cleaning of the clams resulted in lower levels of inorganic arsenic. ODFW collected additional softshell clams in April 2015, and the clams were gathered from a subset of the locations sampled earlier in 2013. Because only arsenic had been found above OHA’s consumption advisory screening levels in 2013, the 2015 samples were only analyzed for total arsenic and inorganic arsenic. The specific sites for the collection of softshell clams in 2015 were selected to represent areas where the clams are normally gathered by recreational clam diggers, and to represent the north coast, mid coast, and south coast. Results from the secondary (April 2015) sampling event confirmed the general findings of the earlier (2013) sampling event. In 2013, elevated levels of inorganic arsenic were detected in geoduck clams (Panopea generosa) in Washington. Subsequent testing by the Washington Department of Health determined that most of the inorganic arsenic detected in Washington geoducks was concentrated in the tough sheath that covers the long siphon. Since softshell clams also have a tough siphon sheath, Oregon agency staff hypothesized that it was likely that the unexpectedly high levels of inorganic arsenic in the softshell clams would also be concentrated in the siphon sheath. To test this hypothesis, a subset of the softshell clams collected in April 2015 was randomly separated and their siphon sheaths removed prior to analysis. These siphon sheaths were then collected and analyzed separately. ODFW also confirmed that most recreational clammers complete this cleaning step prior to consumption. As hypothesized, softshell clams without siphon sheaths exhibited much lower levels of inorganic arsenic in comparison with co-located clams with intact siphon sheaths. In addition, siphon sheaths analyzed separately had much higher concentrations of inorganic arsenic, further confirming the hypothesis that removal of the siphon sheath results in substantially decreased levels of inorganic arsenic. 4 Finalized June 2015 Assessment Sample Collection Summary – In the summer of 2013, ODFW and DEQ collected 20 bivalve mollusk samples. Each of the 20 samples was a composite of several bivalve mollusks of the same species. The average number of individuals per composite was 20. Four species were sampled, soft-shell clams (Mya arenaria), California mussels (Mytilus californianus), Olympia oysters (Ostrea lurida), and purple varnish clams (Nuttallia obscurata). Samples were whole-body, excluding the shells but including contents of the digestive tracts. The samples were divided by geographical regions: North Coast, Mid-Coast, and South Coast. The North Coast included sampling areas in Netarts Bay, Necanicum River mouth (Seaside), Nehalem Bay, Tillamook Bay, and the Columbia River Estuary - South Jetty. Mid-Coast sampling areas included the Siuslaw River mouth, Yaquina Bay, Siletz Bay, Alsea Bay, and Bob Creek. South Coast sampling areas included Bailey Beach, Bastendorf Beach, Coquille River, Ferry Creek, and Coos Bay. Not all species were sampled at all sites since sampling locations were often in habitats specific to certain species. Given concerns about unusual inorganic arsenic findings in softshell clams detected during the 2013 sampling event, an additional 8 composite samples of softshell clams were collected in April 2015, averaging 30 individuals per composite. The 2015 clams were randomly separated into two groups: (1) Group 1 was composed of clams with intact siphon sheaths; and (2) Group 2 was composed of clams from which the siphon sheaths had been removed. The individuals in each group were then aggregated and composited for analysis. The samples of clams without siphon sheaths (Group 2) numbered 8 composite samples in total and averaged 20-30 individuals per composite. Tables 2-4 summarize the sampling effort for the softshell clams collected during the 2013 – 2015 sampling events. For softshell clams, data from 2013 and 2015 are combined. Other species were only collected in 2013. Table 2. North Coast shellfish sampling effort (2013-2015 sampling events) Species Number of organisms Number of composites Number of organisms per composite Softshell clams (whole body) 88 Softshell clams (no siphon sheath) 44 California Mussels Olympia Oysters Purple Varnish Clams 20 114 None 6 3 1 1 --- 10-24 10-24 20 114 --- 5 Finalized June 2015 Table 3. Mid Coast shellfish sampling effort (2013-2015 sampling events) Species Softshell clams (whole body) Number of organisms Number of composites Number of organisms per composite 88 Softshell clams (no siphon sheath) 42 8 6-20 California Mussels Olympia Oysters Purple Varnish Clams 34 None 20 4 2 --- 1 6-20 17 --- 20 Table 4. South Coast shellfish sampling effort (2013-2015 sampling events) Species Softshell clams (whole body) Number of organisms Number of composites Number of organisms per composite 140 Softshell clams (no siphon sheath) 30 6 20-30 California Mussels Olympia Oysters Purple Varnish Clams 37 Unknown None 1 2 1 --- 30 12-25 Unknown --- Table 5 summarizes the averages and variability in the weights of individual clams, mussels, and oysters. Individuals were not weighed prior to compositing, so individual weights were calculated by dividing the total sample weight by the number of individuals in the composite sample. Body weights for individual softshell clams averaged 16.12 grams/clam with high variability ranging from 7.52 to 31.17 grams/clam. California mussels averaged 15.9 grams/mussel with high variability ranging from 7.58 to 29.13 grams/mussel. Individual weights could only be calculated for one composite sample each for Olympia oysters (2.9 grams/oyster) and purple varnish clams (10.73 grams/clam). Table 5. Body weights for individual clams, mussels, and oysters; weights indicated are for wet tissue, exclusive of the shells Species Softshell clams California mussels Olympia oysters Purple Varnish Clams Average weight (grams/individual) 16.12 15.90 2.69 (represents one sample) 10.73 (represents one sample) Standard Deviation (grams/individual) 7.08 8.10 --- Range (grams/individual) 7.52 – 31.17 7.58 – 29.13 --- --- --- 6 Finalized June 2015 Analysis - All species of shellfish collected in 2013 were tested for metals including total and inorganic arsenic, mercury, cadmium, and selenium. Organic analytes included chlorinated pesticides, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), dioxins and furans, and organic tin compounds. We compared maximum and average tissue concentrations of each analyte against its screening value (see Target Analytes for Oregon Fish Advisory Program [Attachment 1]) for each species and for each region (i.e., North Coast, Mid Coast, and South Coast). Inorganic arsenic was the only analyte to exceed its screening value in any species at any location. Dioxins were nondetectable except in 4 samples (two softshell clam samples and two oyster samples). One softshell clam sample came within 50 percent of the screening value for dioxins, while the rest were less than the screening value by more than an order of magnitude. For California mussels and oysters, state-wide average cadmium concentrations came within 38% of the cadmium screening value, but no samples exceeded 48% of, or exceeded the screening value. In all other species, cadmium levels were more than an order of magnitude below the screening level for this analyte. No other analytes had average concentrations within an order of magnitude of their screening values. This analysis indicates that inorganic arsenic is the primary contaminant of concern for shellfish along the Oregon coast. The analysis also indicates that the level of inorganic arsenic only exceeded the screening value in softshell clams when the siphon sheaths were intact. The levels of inorganic arsenic were well below the screening level when the siphon sheaths were removed from the softshell clams. No other species exceeded the screening level for inorganic arsenic. Average inorganic arsenic concentrations did not come within an order of magnitude of the screening value in any species other than softshell clams. Softshell clams Table 6 summarizes inorganic arsenic levels for three regions of the Oregon coast for softshell clams with intact siphon sheaths. Table 7 summarizes inorganic arsenic levels for the three regions of the coast for softshell clams without siphon sheaths. In all cases, removal of the siphon sheath resulted in a substantial decrease in the inorganic arsenic to a level well below the screening value of 0.7 mg/kg. Note that there was only one composite sample for softshell clams without siphon sheaths in the South Coast. This composite contained 30 individuals. Because only one composite sample was available, no summary statistics could be generated. We calculated meal recommendations for this group based on the result of the single composite sample. While it is not ideal to base a meal recommendation on a single composite sample, the result of that one sample aligns well with expectations based on the lower inorganic arsenic in whole body softshell samples from the same region. This adds confidence to the results obtained from the single sample. A wide variety of peoples and cultures dig clams from the Oregon Coast. With such a variable population to consider, we relied on EPA default values for the body weight of humans (70 kg) to calculate allowable consumption rates. We also used the EPA Oral Reference Dose (RfD) for inorganic arsenic (0.0003 mg/kg-day). The oral RfD is an estimate of daily exposure to the human population (including sensitive sub-groups) that is likely to avoid deleterious effects during a lifetime. The RfD of 0.0003 mg/kg-day for inorganic arsenic has been identified to protect the general population from potential adverse health effects. 7 Finalized June 2015 Table 6. Inorganic arsenic in softshell clams with intact siphon sheaths Parameters North Coast Mid Coast South Coast Units Mean 4.87 1.38 0.77 mg/kg Standard Deviation 4.95 1.4 0.76 mg/kg Median 5.94 1.44 0.71 mg/kg Minimum 0.54 0.29 0.27 mg/kg Maximum 8.3 2.98 1.15 mg/kg N Samples 6 8 6 Composite Samples N clams 88 88 140 # Clams Skin on meals/month 1 2 4 meals/month Note: Values displayed here are rounded to the second post-decimal, non-zero digit. All digits were used in calculations. Meal recommendations were rounded to the nearest whole meal. Table 7. Inorganic arsenic in softshell clams without siphon sheaths Parameters North Coast Mid Coast South Coast Units Mean 0.26 0.11 0.084 mg/kg Standard Deviation 0.20 0.089 NA mg/kg Median 0.22 0.060 NA mg/kg Minimum 0.12 0.047 NA mg/kg Maximum 0.33 0.16 NA mg/kg N Samples 3 4 1 Composite Samples N clams 44 42 30 # Clams Skin off meals/month 11 26 33 meals/month Note: Values displayed here are rounded to the second post-decimal, non-zero digit. All digits were used in calculations. Meal recommendations were rounded to the nearest whole meal. NA = Not available because only one composite sample was collected. Results The intact bodies of softshell clams (Mya arenaria) on the Oregon Coast contain inorganic arsenic at levels that can be harmful to human health. The inorganic arsenic is concentrated in the siphon sheath. The level of inorganic arsenic in clam tissue is reduced below the screening level when the siphon sheath is removed. Removal of the siphon sheath decreased the level of inorganic arsenic by a factor of 18.7 for the softshell clams collected from the north coast, by a factor of 12.5 for the mid coast, and by a factor of 9.2 for the south coast. On average, removal of the siphon sheath reduced the level of inorganic arsenic by a factor of 13.5. Clam diggers should be advised to properly prepare softshell clams by removing the siphon sheath prior to consumption. The siphon sheath of softshell clams contains grit and sand, and this tough tissue is normally discarded during preparation and cleaning. Humans do not normally consume the siphon sheaths of softshell clams. The recommended advisory for the Oregon Coast, based on the assessment above, is shown in Table 8 below. The advisory has been approved by technical and managerial staff from OHA. Note that meals/month is rounded to the nearest whole meal per month. 8 Finalized June 2015 Table 8. Meal Recommendations for Softshell Clams harvested along the Oregon Coast Coast Segment North Coast (mouth of Columbia to Neskowin) Mid Coast (Cascade Head to mouth of Umpqua River) South Coast (mouth of Umpqua River to California border) Shellfish Types Softshell Clams (with intact siphon sheath) Recommended meals/month 1 Risk-driving contaminant Inorganic Arsenic Softshell Clams (without siphon sheath) Softshell Clams (with intact siphon sheath) 11 Inorganic Arsenic 2 Inorganic Arsenic Softshell Clams (without siphon sheath) Softshell Clams (with intact siphon sheath) 26 Inorganic Arsenic 4 Inorganic Arsenic Softshell Clams (without siphon sheath) 33 Inorganic Arsenic Comments DEQ Data from 2013 and 2015 Meal sizes are scaled to the body weight of humans. Table 9 gives the appropriate meal sizes for children broken down into different age groups. The bodies of softshell clams have a density basically equal to water. Therefore, meal weights in ounces are equal to volume in ounces (all weights and volumes refer to edible tissue excluding shells). The size of individual clams is highly variable (see table 5) and hampers development of a reliable correlation between number of clams and meal size. Table 9. Meal sizes for different age groups of humans Age Group Adult (16 years and older) 11-16 years old 6-11 years old 3-6 years old 2-3 years old Meal size by weight (excluding shells) 8 ounces 6 ounces 4 ounces 3 ounces 2 ounces Meal size by volume (excluding shells) 1 cup ¾ cup ½ cup 1/3 cup ¼ cup Discussion The recommended meal limits for softshell clams collected along the Oregon coast is presented in Table 8. Given the available dataset, this advisory represents a rigorous approach that is most protective of human health. In the event that additional data become available in the future, especially for other species, OHA will evaluate those data and update this advisory as indicated by the data. If more softshell 9 Finalized June 2015 clam samples are collected in more popular clamming areas, the geographical extent of the advisory could also be further refined. This advisory will be accompanied by graphics and public messaging to describe how to remove the siphon sheath from softshell clams. These materials will be developed in collaboration with ODFW. Once this technical memo is approved, staff will begin the joint development of communication and outreach plans and materials. Limitations Some uncertainties exist in any scientific process. For the 363-mile stretch of the Oregon coastline, there are insufficient resources to capture enough samples to comprehensively represent the entire coast. It is possible that we are over- or underestimating the true average tissue concentrations of contaminants in Oregon shellfish. However, the available data provide sufficient evidence to support the protective health actions recommended in this advisory. Our use of the arithmetic mean assumes that clam diggers, over a lifetime, will dig a random distribution of clams over the entire segment of the coast covered by an advisory. This may or may not reflect the actual practice of clam diggers along the coast. It is possible that a clam digger consistently collecting from one particular spot over a lifetime could get clams that are consistently higher or lower than the mean used to calculate this advisory. 10 Finalized June 2015 Attachment 1 Oregon Health Authority Standard Operating Guidance Target Analytes for Oregon’s Fish Advisory Program December 30, 2013 Chemical Form Oral Reference Dose1 (mg/kg-day) Screening Value (mg/kg fish tissue) Inorganic 0.0003 0.7 0.001 2.3 Metals Arsenic Cadmium Mercury (Vulnerable Populations)2 Methylmercury 0.0001 0.2 Mercury (General population)3 Methylmercury 0.00034 0.6 Selenium 0.005 11.7 Tributyltin 0.0003 0.7 0.00003 0.07 Organochlorine Pesticides Aldrin 1 Unless otherwise noted, all oral reference doses are from EPA’s IRIS program (http://www.epa.gov/IRIS/) Vulnerable populations are children and women of childbearing age 3 General public excluding vulnerable populations (defined above) 4 This value is based on an older IRIS value for methylmercury, which was based on studies in otherwise healthy adults. This value is used in this way by state fish advisory programs in California, Washington, and Idaho. See Technical Memo on the Use of an Alternate Toxicity Value for Methylmercury Applied to Healthy Adults. 2 11 Finalized June 2015 Chemical Form Oral Reference Dose1 (mg/kg-day) Screening Value (mg/kg fish tissue) Chlordane total (cis- and transchlordane, 0.0005 1.2 0.0005 1.2 Dicofol 0.0004 0.9 Dieldrin 0.00005 0.1 0.006 14 Endrin 0.0003 0.7 Heptachlor Epoxide 0.00001 0.03 Hexachlorobenzene 0.0008 1.9 0.0003 0.7 Methoxychlor 0.005 11.7 Mirex 0.0002 0.5 Toxaphene5 0.002 4.7 Chlorpyrifos 0.0003 0.7 Diazinon 0.0007 1.6 cis- and trans-nonachlor, oxychlordane) DDT total (2,4’-DDD, 4,4’-DDD, 2,4’-DDE, 4,4’-DDE, 2,4’-DDT, 4,4’DDT) Endosulfan Lindane I and II γ-hexachlorocyclohexane; γ-HCH Organophosphate Pesticides 5 ATSDR’s Intermediate Oral Minimal Risk Level (http://www.atsdr.cdc.gov/toxprofiles/tp94-a.pdf ); no IRIS value 12 Finalized June 2015 Oral Reference Dose1 (mg/kg-day) Screening Value (mg/kg fish tissue) Disulfoton 0.00004 0.09 Ethion 0.0005 1.2 Terbufos 0.00002 0.05 0.003 7 Chemical Form Chlorophenoxy herbicides Oxyfluorofen Polychlorinated biphenyls (PCBs) Total (sum of congeners) 0.00002 0.05 Dioxins/furans TEQ 0.0000000007 1.6 (ng/kg) Brominated flame retardants Congener-specific analysis BDE-47 0.0001 0.2 BDE-99 0.0001 0.2 BDE-153 0.0002 0.5 BDE-209 0.007 16.3 Perfluorooctane Sulfonate (PFOS) 0.00008 0.2 Perfluorooctanoic Acid (PFOA) 0.00008 0.2 Perfluorochemicals (PFCs)6 Congener-specific analysis 6 PFC RfDs developed by Minnesota Department of Health (http://www.health.state.mn.us/divs/eh/hazardous/topics/pfcs/finalreport011508.pdf); no IRIS value available 13 Finalized June 2015 Screening values were developed from the listed RfD assuming 4 eight-ounce fish meals per month using the equation below: Where: SV = Screening value (mg/kg) RfD = Oral reference dose (mg/kg-day) BW = Bodyweight (70 kg for all but mercury which used 60 kg for pregnant women) IR = Intake rate of fish (30 grams per day) CF = Unitless conversion factor (0.001) to convert grams of fish to kilograms of fish 14