119°W 



40- 



20' 



118°W 



FliilRK 1. — Outfall and island control sites ofT Los Angeles, 

 Calif., for collection of rock scallops. 



solution (ultrahigh-purity reagent grade) until 

 the remaining volume was about 3 ml. This proce- 

 dure was repeated once, and the final residue was 

 filtered through an acid-washed Whatman No. 40 

 filter. The filtrate was then diluted to an appro- 

 priate volume, and the treated sample was 

 analyzed by atomic absorption spectrometry. 

 Silver, chromium, copper, nickel, and lead were 

 measured by injecting 2.5 /u,l of sample into a 

 graphite furnace; cadmium and zinc levels were 

 determined by aspirating the sample into an air- 

 acetylene flame. 



Process blanks were analyzed with all samples. 

 Typical blank corrections were <l(y7( of the gross 

 concentrations observed, except for chromium, 

 nickel, and zinc in adductor muscle, where the 

 blank corrections were 15-20^ of the gross con- 

 centrations. To test digestion efficiency, residues 

 collected after filtration were redigested following 

 the same procedure employed initially but using 

 only 5 ml of 1:1 nitric acid solution; levels mea- 

 sured in the residue generally were <5'7( of the 

 concentrations found in the first digestion. In ad- 

 dition, using this procedure on Standard Refer- 

 ence Material No. 1571 (orchard leaves) we have 

 obtained values for our target metals which are 

 within the ranges reported by the National 



Bureau of Standards ( NBS); in all cases our results 

 agreed within ±20% of the NBS values. 



Results and Discussion 



A comparison of the 1974 and 1976 results indi- 

 cated that, for each of the seven metals studied, 

 there were no significant differences between 

 levels in the Palos Verdes scallops collected during 

 the 2 yr. Therefore, the data from these 16 speci- 

 mens have been combined to obtain an estimate of 

 metal concentrations in scallops around the 

 JWPCP submarine outfalls (Table 1). However, 

 distinctly higher levels of silver, chromium, and 

 copper were measured in the specimens from the 

 other two coastal stations, compared with those in 

 the scallops from the island control sites. Alexan- 

 der and Young ( 1976) also observed elevated con- 

 centrations of these three metals in digestive 

 glands of the intertidal mussel Mytilus califor- 

 nianus collected within 100 km of Los Angeles, 

 indicating the widespread influence of municipal 

 wastewater discharges on distributions of silver, 

 chromium, and copper in the nearshore marine 

 ecosystem of southern California. Therefore, we 

 have used only the data from the six island speci- 

 mens to estimate natural concentrations of the 

 target trace metals in the three scallop tissues 

 investigated (Table 1). For each metal we have 

 calculated a "contamination factor," defined as the 



Table l. — Trace metal concentrations (mg/wet kg) in tissues of 

 rock scallops collected during 1974-76 from the Palos Verdes 

 outfall zone (16 specimens) and from island control stations (6 

 specimens). Single and double asterisks indicate experimental 

 results are significantly different from control results atP<0.05 

 andP<0.01, respectively.' 



'Determined by the nonparametric 2-sided Mann-Whitney U Test. 



937 



