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Turner, A., Millward, G. E. & Morris, A. W. (1991). Particulate metals in five major North Sea estuaries. Estuar. Coast. Shelf Sci. 32, 325-346. Van Alsenoy, V., Bernard, P. & Van Grieken, R. (1993). Elemental concentrations and heavy metal pollution in sediments and suspended matter from the Belgian North sea and Scheldt Estuary. Sci. Tot. Environ. 133, 153-181. Wheeler, A. C. (1979). The Tidal Thames. The History of a River and its Fishes. Routledge and Kegan Paul, London. Wood, L. B. (1980). The rehabilitation of the tidal River Thames. Publ. Hlth Engr. 8, 112-120. MarinePollutionBulletin, Vol.30, No. I1, pp. 744-745,1995 Pergamon Elsevier Science Ltd Printedin GreatBritain 0025-326X(95)00156--5 DDT in California Sea-Lions: A Follow-Up Study After Twenty Years PATRICIA LIEBERG-CLARK, CORINNE E. BACON, STEPHANIE A. BURNS, WALTER M. JARMAN* and BURNEY J. LE BOEUF Institute of Marine Sciences, Earth and Marine Science Building, University of California, Santa Cruz, CA 95064, USA *Author to whom correspondence should be addressed. Extraordinarily high levels of EDDT (p,p'-DDT+p,p'- DDD+p,p'DDE) have been reported previously in California sea-lions (Zalophus californianus california- nus) collected on the central California coast in the early 1970s (Le Boeuf & Bonnell, 1971). We now report a decrease of over two orders of magnitude in YDDT levels in California sea-lions between 1970 and 1992. In no other wildlife population has such a large decline in residue levels been reported (Loganathan & Kannan, 1991). As with brown pelicans (Pelecanus occidentalis), this decline in levels is attributed to the cessation of the release of DDT residues by the Montrose Chemical Corporation (Anderson et al., 1975). The decline in residue levels in California sea-lions over this period is accompanied by a significant increase in the population during the same time period. Blubber tissue was collected from fresh carcasses of sub-adult and adult male sea-lions found on beaches between Afio Nuevo Point in San Mateo County and the Pajaro River mouth in Santa Cruz County, California, between April 1988 and July 1992. The blubber samples weighed 40-50 g, and were frozen immediately. The samples were extracted with CH2Cl2:hexane (1:1), fractionated and analysed by dual column high resolution gas chromatography. A detailed description of the method can be found in Jarman et al. (1993). Levels are reported in mg kg-1 wet weight, as geometric means. The mean level of EDDE for adult and sub-adult male California sea-lion samples in the present work was 5.0 mg kg-l (n = 7), compared to 740 mg kg-1 for 12 sea-lion samples in 1970 (Table 1). This is a significant (/7<0.0001) decline of over two orders of magnitude, p,p'-DDE and p,p'-DDT were found in all samples from both studies. A small amount of p,p'- DDD may also have been present in some or all of the samples, but could not be quantified because of co- elution with cis-nonachlor (the p,p'-DDD concentra- tions for both data sets are considered negligible with respect to the ]EDDT value). Addison (1989), in a review of organochlorine and marine mammal reproduction, suggested that the levels of ~.DDT reported in 1971 might be artificially high due to eo-elution with PCB compounds. The main inter- ference of PCBs with the quantification of DDT compounds in marine mammals is the co-elution of p,p'-DDT with PCBs (Risebrough, 1969). The 1970 data did not show an abnormally high DDT:DDE ratio (Table 1) and the high levels of EDDT were similar to TABLE 1 Geometric mean levels of DDE,' DDT, and the ratio of DDT/ DDE( x 100) in male California sea-lion blubber, with a range of one SD in parentheses. Residue values are expressed as mg kg-" wet wt. DDE 1970" 1988-1992 DDT DDT/DDE DDE DDT DDT/DDE 740 17 0.023 5.0 0.16 0.032 (370-1500) (8.8-34) (2.5-10) (0.07-0.35) n=12 n=7 "1970 data were originally reported as arithmetic means (Le Boeuf & Bonnell, 1971). 744