EXCEEDANCES OF PUBLIC HEALTH LIMITS 



Concentrations were placed in the "high" category on the basis of their magnitude relative to other 

 concentrations. There is no reason to suppose that such concentrations cause harm to marine organisms 

 or to man. With two exceptions at single sites, lead is the only chemical measured in the Mussel Watch 

 Project whose concentration was above a public health guideline. 



There are U.S. Federal Drug Administration standards* for chlorinated hydrocarbons and for mercury, 

 such that fish and shellfish with higher concentrations are prohibited from interstate commerce. None 

 of the standards are exceeded for mercury, XDDT, Zdieldrin, or Xchlordane at any site in any year. The 

 10,000 ng/g (dry-weight) standard for ZPCB was exceeded in 1989 at one site in Buzzards Bay, MA 

 but not in any other year. In 1993, the FDA issued human consumption guidelines for concentrations of 

 five trace elements in moUuscan and crustacean shellfish that vary with the age of consumer and rate 

 of consumption. For three of those elements, arsenic, chromium, and nickel, there are no cases where 

 mussels or oysters collected in the Mussel Watch Program exceeded even the most stringent guideUne. 

 In 1991, the only year it was successfully sampled, the site in Lake Pontchartrain near New Orleans 

 yielded oysters whose cadmium concentrations exceeded the lowest guideline. 



For Pb there were many exceedances. The FDA guidelines converted to a dry weight basis are: 



Consumption rate 

 Group Mean Upper 90th percentile 



Children (2-5) 7.5 ppm-dry 4.0 ppm-dry 



Pregnant women 10.5 7.0 



Adults 31.5 21.0 



The last of the figures on spatial distribution of high concentrations is for lead (Fig. 15), and is based on 

 a "high" concentration of 4 ppm. This value is close to the "high" for mussels but is also the lowest 

 public health guideline, applicable to children consuming mollusks at a rate of 8 grams per day. It is 

 evident on Table 4 that progressively fewer sites have mollusks with concentrations at the higher guideUne 

 levels. The distribution of sites with high lead concentrations is like those for organic contaminants and 

 mercury in that, for the most part, high concentrations are found in the vicinity of population centers. 

 So, as with those chemicals, high concentrations are attributable to human activities. 



TEMPORAL TRENDS 



Chemical concentrations in mussels and oysters are determined by the extent to which the organisms 

 accumulate chemicals from the food they filter out of their surrounding water and from the water itself. 

 When chemical concentrations increase or decrease in their surroundings, the organisms are capable of 

 increasing or decreasing the corresponding concentrations in their tissues (see for example, Roesijadi 

 et al., 1984; Pruell et al., 1987). This, and the fact that they are immobile, make them ideal for monitor- 

 ing changes in chemical concentrations at fixed sites. 



A trend is a correlation between concentration and time. Over a time span as short as eight years, we 

 are not likely to decipher cycles in concentrations, so the trends sought in the Mussel Watch data are 

 linear correlations between ranks of concentration and time. Specifically, the data are examined to see 

 if concentrations are changing in a single direction, up or down. 



FDA guidelines are given as concentrations on a wet- weight basis. They have been multiplied by five 

 for application to Mussel Watch data which are concentrations in terms of dry-weight. This uses the 

 conventional assumption that the soft-parts of organisms are 80% water by weight. (Actually, mussels 

 and oysters average closer to 85% water which would require multiplying the criteria by 7.5 and, in 

 effect, finding fewer public health exceedances than would the conventional assumption.) 



