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My Water Quality: Thresholds and Advisories

Fish & Shellfish Tissue Thresholds and Advisories

Preparing fish

What are OEHHA's assessment thresholds?

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The Cal/EPA Office of Environmental Health Hazard Assessment (OEHHA) developed Advisory Tissue Levels (ATLs) and Fish Contaminant Goals (FCGs) for different purposes. Both benchmarks are expressed as concentrations of a specific chemical in fish tissue to which people could be exposed when eating sport fish. OEHHA developed ATLs and FCGs for seven chemicals: chlordane, DDTs, dieldrin, mercury, PCBs, selenium, and toxaphene. Multiple ATLs were developed for each chemical showing a range of contaminant rates where fish consumption can be recommended at 3, 2, or 1 servings per week, or no consumption.  For mercury, separate ATLs were derived for more sensitive sub-populations (women 18 to 45 years of age and children 1 to 17 years) and others (men over 17 years of age and women over 45 years). ATLs balance the benefits of eating fish with the risks from contaminants they may contain.

OEHHA developed Fish Contaminant Goals (FCGs) for agencies using criteria values for management decisions, but without the same public health mandates as OEHHA. A single FCG was developed for each of the seven chemicals named above. These values are purely risk-based and are intended to be used to develop water quality criteria or cleanup levels. More >>

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How does OEHHA develop fish consumption advisories and safe eating guidelines?

OEHHA is responsible for issuing fish consumption advisories and safe eating guidelines. OEHHA staff developed ATLs as a starting point in the process to develop consumption advice. ATLs are not absolute values that always lead to the same fish consumption recommendation. Other factors are considered (for example, levels of beneficial omega-3 fatty acids, the distribution of contaminant levels, and how to simplify communication) before OEHHA issues consumption advice. OEHHA’s ATLs, as well as advisories and safe eating guidelines based on them, balance the risks and benefits from fish consumption. FCGs are not used to develop advisories. More >>

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Why do so few water bodies have fish consumption advisories and safe eating guidelines?

For OEHHA to be able to issue fish consumption advisories or safe eating guidelines, data are needed from a significant number of fish tissue samples representing a variety of fish species present in a body of water. Most screening studies do not generate sufficient data for OEHHA to issue fish consumption advisories. To alleviate this issue with lakes and reservoirs, OEHHA issued a general advisory for California lakes and reservoirs that do not have site-specific advice.

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What thresholds are used in Water Board SWAMP screening study reports?

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SWAMP screening study reports, published by the State Water Resources Control Board, have combined OEHHA’s ATLs and FCGs in a series of thresholds and used them to provide a frame-of-reference for study results. These values have not formally been adopted and have not triggered additional specific actions. References to specific consumption categories (e.g., a serving per week) in these reports should not be used as consumption recommendations. In addition the Water Boards use the current EPA Clean Water Act 304(a) recommended criteria document to establish a threshold/benchmark of 0.3 ppm for methylmercury based on a protective human health default consumption rate of 17.5 grams per day.

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What thresholds are used to list a water body as "impaired"?

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Section 303(d) of the federal Clean Water Act (CWA) requires states to identify waters that do not meet applicable water quality standards with technology-based controls alone and prioritize such waters for the purposes of developing Total Maximum Daily Loads (TMDLs). The States are required to evaluate all existing readily available water quality data and information to develop the list. The methodology to be used to develop the Section 303 (d) list is established in California Water Quality Control Policy (Listing Policy). In order to make decisions regarding standards attainment, the Listing Policy provides guidance for interpreting data and information as they are compared to beneficial uses, existing numeric and narrative water quality objectives and anti degradation considerations. Narrative water quality objectives are evaluated using evaluation guidelines. The Regional Water Quality Boards have the flexibility to identify appropriate evaluation guidelines for their regions that represent standards attainment or beneficial use protection. The thresholds developed by OEHHA may or may not be used for this purpose. In addition to the thresholds developed by OEHHA, the Water Boards have used exceedance of the U.S. EPA’s current Clean Water Act 304(a) recommended criteria for methylmercury as a benchmark for section 303 (d) listing of impaired waterbodies.