This Guidance document represented current agency thinking in regards to the available science at the time it was issued. It no longer represents the current state of science and is presented here for the historical record only.

Guidance Document for Arsenic in Shellfish

Center for Food Safety and Applied Nutrition

United States Food and Drug Administration
200 C St., S.W.
Washington, D.C. 20204
January 1993

This document has been developed to satisfy requests from local and state officials for federal guidance regarding the public health significance of arsenic in shellfish. (The term "shellfish" is used in a general sense throughout this document and is meant to include both molluscan bivalves and crustacea.) This document is designed to assist local and state health officials in their deliberations concerning the possible need to either issue consumption advisories or to close waters for fishing because of excessive arsenic contamination. The contents of this document include sections on FDA's statutory authority, a public health statement, sampling techniques and trace element analysis, consumption and exposure information, hazard assessment, and a discussion of estimating levels of concern for local consumption advisories or water closures.

Arsenic and its compounds are widely distributed in nature primarily in two oxidation states, arsenite (trivalent) and arsenate (pentavalent). Inorganic and organic arsenic compounds used as pesticides, plant defoliants, and herbicides may accumulate in agricultural and horticultural soils and plants. Traces of arsenic are found in most foods, with the highest concentrations found in seafood, particularly in shellfish, at total arsenic levels up to 30 g/g wet weight. Nearly all of the arsenic present in seafood is organic arsenic which is considered to be much less toxic than inorganic arsenic. It is estimated that in the U.S. the mean total arsenic intake from all food (excluding shellfish) is approximately 30 g/person/day.

Inorganic arsenic can have acute, subacute, and chronic effects. Based on the provisional maximum tolerable weekly adult intake for inorganic arsenic recommended by the WHO/FAO (15 g/kg/week) for short term or chronic exposures, this document recommends a tolerable daily intake of inorganic arsenic of 130 g.

Surveys of contaminants in shellfish conducted by FDA and the National Marine Fisheries Service have found mean total arsenic levels 1.1 ppm to 30 ppm (wet weight basis). FDA has combined these survey results with nationally representative shellfish consumption information to estimate the range of total arsenic exposures that are possible among shellfish consumers. For individuals who chronically consume an average of 15 g/day of molluscan bivalves (90^th percentile average intake over 14-days for consumers among survey population) that have mean total arsenic levels of 3.8 ppm, total arsenic intake will average 57 g/person/day. For people consuming an average of 17 g/day of crustacean shellfish (90^th percentile average intake over 14-days for consumers among survey population) that contain mean total arsenic levels of 10.6 ppm, total arsenic intake will average 180 g/person/day.

Although the tolerable daily intake for arsenic is based on exposure to inorganic arsenic, most arsenic present in shellfish is in an organic form (which is relatively non-toxic) and most monitoring methods determine total arsenic. To use traditional monitoring results to evaluate acceptable levels of shellfish consumption or acceptable levels of arsenic contamination, an estimation procedure that assumes that inorganic arsenic accounts for only 10% of the arsenic in shellfish is proposed for converting measurements of total arsenic to estimates of inorganic arsenic. It is proposed that this estimation procedure be used in lieu of monitoring results that are specific for inorganic arsenic.

Local patterns of shellfish consumption and/or the levels of arsenic contamination may vary from national averages. Hence, arsenic exposures from shellfish in particular regions may also vary from values estimated using national figures. In order to decide whether local arsenic exposure levels are of concern, it is suggested that the maximum tolerable daily intake for inorganic arsenic (130 g/person/day) be used to calculate Levels of Concern, either maximum permitted amounts of chronic shellfish consumption or maximum permitted levels of arsenic contamination.

Although local figures for shellfish consumption or shellfish contamination would be most appropriate for evaluating local situations, reference to national figures may also prove useful. As an example, if it is assumed that total arsenic exposure is derived solely from shellfish, it is calculated that the arsenic level of concern for individuals consuming molluscan bivalves on a chronic basis at the 90^th percentile average among eaters (15 g/person/day) would be 86 ppm. The corresponding consumption level of concern for individuals consuming molluscan bivalves with total arsenic levels equivalent to the highest average found in one of the national surveys (3.8 ppm) is 340 g/person/day. If other sources of inorganic arsenic exposure are to be considered (e.g., relative source contribution including other dietary sources of arsenic), then corresponding adjustments in the levels of concern will need to be made.