MacGREGOR: DDT OFF SOUTHERN CALIFORNIA 



►'«•.. 



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O o o o 



FIGURE 6.— Stations at which the ratio of o,p' DDT top.p'DDT 

 was greater than 0.40:1.00. 



Figure 7. — Stations at which the ratio of o,p' DDD to 

 p,p 'DDD was greater than 0.40:1.00. 



To estimate the amount of DDT stored in the 

 bottom sediments in the approximately 911 sq 

 nautical miles between long. 117°58' and 

 118°46'W and lat. 33°18'N and the California 

 coast, represented by the 103 stations, we must 

 assume that each station is representative of its 

 surrounding area. Each pair of samples from each 

 station showed a high correlation for all pairs of 

 parameters. The correlation coefficient for the 

 logarithms of total DDT for paired samples from 

 94 stations from which two samples were ob- 

 tained was 0.964 and the standard error of esti- 

 mate ±0.321. 



The Shipek sampler took bottom silts only to a 

 depth of about 10 cm and sandy bottoms or shal- 

 low sediment deposits to a lesser depth. At all 

 stations except those where bottom deposition 

 was very rapid, as near sewer outfalls, all DDT in 

 the sediments was sampled. Near the sewer out- 

 falls the sample represents only DDT deposits in 

 the top 10 cm of sediment. The total amount of 

 DDT determined for the 911 sq nautical mile 

 sampling area was 217 metric tons in the top 10 

 cm of bottom sediment. Of this total, 179 metric 

 tons (82%) was DDE, 22 metric tons (10%) was 

 DDD, and 16 metric tons (8%) was DDT. McDer- 

 mott and Heesen (1974) found that the total DDT 

 in the top 5 cm of sediment consisted of 86% DDE, 

 11% DDD, and 3% DDT in the area of the Palos 

 Verdes shelf These somewhat different percent- 

 ages may have resulted from further metabolism 

 of DDT without replenishment. In addition, the 

 DDE percentages tend to be higher in this area, 

 and the DDD was increased in 1970-71 because of 

 sewer cleaning operations. 



The total DDT ranged from an estimated 0.42 

 kg per sq nautical mile at station 30-08 repre- 

 senting 13.3 sq nautical miles to 28.6 metric tons 

 per sq nautical mile at station 43-22 representing 

 1.25 sq nautical miles. 



Five stations representing 6.24 sq nautical 

 miles or 0.7% of the 911 sq nautical mile area 

 represented by the 103 stations contained 47.3% 



Figure 8.— Stations at which the ratio of o,p' DDE to p,p' DDE 

 was greater than 1.00:1.00. The high apparent o.p'DDE values 

 probably were caused by DDMU which has the same retention 

 time as o,p 'DDE on the column used. 



33 



