concentrations of lead were higher in the 

 1970s. The preponderance of change in 

 that direction indicates a decreasing trend 

 that was attributed to the phaseout of 

 leaded gasoline. Yet, when the Sign test 

 was applied to Mussel Watch data be- 

 tween 1986 and 1990 at 141 sites (Table 

 3 ). it failed to detect a trend. This may be 

 due to the fact that the major effect of 

 human intervention occurred in the 

 1970s, and that trends occurring in the 

 1 980s are smaller and more easily masked 

 by natural effects on interannual varia- 

 tion. 



1970s were compared with data from 

 the 1980s. Robinson etal.( 1990) exam- 

 ined data from analyses of human fat 

 tissues collected from autopsies or from 

 surgical patients in 1972 through 1983, 

 and found a large decrease in the early 

 70s, followed by a more-or-less steady 

 decrease to 1983, in the percentage of 

 tissue samples containing more than 

 1 .000 ng/g of tPCB. All of these reports 

 reveal long-term decreases in tPCB in 

 the tissues of organisms, but in all cases, 

 the decreases are made evident over 

 decadal time scales. 



Large annual changes in past decades, 

 followed by smaller shifts in the present 

 day, are common in concentrations of 

 organochlorine compounds. Figure 7, 

 from O'Connor ( 1 990), is a 1 9-year record 

 of tPCB in mussels at the Mussel Watch 

 site off Royal Palms Park on the Palos 

 Verdes coast of Los Angeles. It is based 

 on three sets of data, including that from 

 the NS&T Program. It shows a dramatic 

 decrease that began in 1971 when PCB 

 use began to be phased out in the United 

 States. The magnitude of the decrease 

 may be magnified by the site's location, 

 within 10 km of a major sewage outfall, 

 but other cases have also documented 

 temporal decreases in chlorinated or- 

 ganic contamination. Sericano et al. 



( 1 990) have combined data from diverse 

 sources to show historical decreases in 

 the average tDDT concentration in oys- 

 ters in the Gulf of Mexico. Suns et al. 



(1991) found decreases in concentra- 

 tions of tDDT and tPCB in fish collected 

 in Lake Ontario when data from the mid- 



CONCLUSIONS 



Data from the NOAA NS&T Mussel 

 Watch Project show more decreases than 

 increases in chemical concentrations 

 between 1986 and 1990. At most indi- 

 vidual sites there are no strong correla- 

 tions between concentration and year, 

 but where correlations are found de- 

 creases outnumber increases. This ten- 

 dency for contamination to decrease is 

 occurrins at the same time that our soci- 

 ety is taking more and more steps to 

 control pollution. It supports the view 

 that the imposition of control technolo- 

 gies and other recent actions to limit 

 contaminant releases have, in general, 

 stemmed the increasing levels of chemi- 

 cal contaminants previously observed 

 in our coastal and estuarine waters. 

 However, with only five years of data, it 

 has not been posible to clearly establish 

 long-term trends and more years of sam- 

 pling are required to distinguish more 



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