Impairments of Memory and Learning in Older Adults Exposed to Polychlorinated Biphenyls via Consumption of Great Lakes Fish

Environmental Health Perspectives, June, 2001 by Susan L. Schantz, Donna M. Gasior, Elena Polverejan, Robert J. McCaffrey, Anne M. Sweeney, Harold E.B. Humphrey, Joseph C. Gardiner

An association between in utero polychlorinated biphenyl (PCB) exposure and impaired childhood intellectual functioning has been reported, but the potential impact of PCB exposure during adulthood on intellectual functioning has received little attention. We assessed the impact of PCBs and other fish-borne contaminants on intellectual functioning in older adults. The subjects were 49- to 86-year-old Michigan residents recruited from an existing cohort. Fish eaters ate [is greater than] 24 lb of sport-caught Lake Michigan fish per year and non-fish eaters ate [is less than] 6 lb of Lake Michigan fish per year. A battery of cognitive tests including tests of memory and learning, executive function, and visual--spatial function was administered to 180 subjects (101 fish eaters and 79 non-fish eaters). Blood samples were analyzed for PCBs and 10 other contaminants. We evaluated cognitive outcomes using multiple regression. PCBs and dichlorodiphenyl dichloroethene (DDE) were markedly elevated in fish eaters. After controlling for potential confounders PCB, but not DDE, exposure was associated with lower scores on several measures of memory and learning. These included the Weschler Memory Scale verbal delayed recall (p = 0.001), the semantic cluster ratio (p = 0.006), and list A, trial 1 (p = 0.037), from the California Verbal Learning Test. In contrast, executive and visual--spatial function were not impaired by exposure to either PCBs or DDE. In conclusion, PCB exposure during adulthood was associated with impairments in memory and learning, whereas executive and visual--spatial function were unaffected. These results are consistent with previous research showing an association between in utero PCB exposure and impairments of memory during infancy and childhood. Key words: DDE, dichlorodiphenyl dichloroethene, executive function, Great Lakes fish, learning, memory, older adults, polychlorinated biphenyls, PCBs, visual--spatial function. Environ Health Perspect 109:605-611 (2001). [Online 5 June 2001]

http://ehpnet1.niehs.nih.gov/docs/2001/ 109p605-611schantz/abstract.html

Great Lakes fish are contaminated with a host of pollutants including chlorinated organic compounds such as polychlorinated biphenyls (PCBs) and dichlorodiphenyl dichloroethene (DDE), pesticides such as mirex and dieldrin, and trace amounts of metals such as lead and mercury. Although commercial fishing on the Great Lakes is subject to federal regulation, sport fishing is not regulated. Advisories have been developed to inform the public about which fish are safe to eat, but the impact of these advisories on fish consumption is unknown.

The health impacts of regular consumption of sport-caught Great Lakes fish are not clear. However, previous studies have reported an association between in utero exposure to PCBs via maternal consumption of Great Lakes fish and impaired intellectual functioning in infancy (1) and childhood (2-4). In these children, the clearest and most consistent negative association between PCB exposure and intellectual function was seen on tests involving verbal competence and short-term memory processing. Recently another team of investigators has reported a similar association between PCB exposure from Great Lakes fish and short-term memory processing in infancy (5). Deficits in intellectual function have also been reported in children whose mothers were exposed to PCBs and related compounds from non-fish sources in the Netherlands (6) and in Taiwan (7). In contrast, no relationship between PCB exposure and childhood intellectual functioning was observed in a cohort of children in North Carolina (8).

The potential impact of PCBs and other fish-borne contaminants on the intellectual functioning of adults has received very little attention. Older adults may be at increased risk from exposure to fish-borne contaminants such as PCBs and DDE because body burdens of these lipophilic compounds increase with age (9). At the same time, many aspects of neurological function decline with advancing age (10). We conducted the present study to determine if exposure to PCBs and other fish-borne contaminants negatively impacts neurocognitive functioning in older adults.

Methods

Sample

The subjects were selected from an existing cohort of people who consumed large amounts of Great Lakes fish (n = 572) or little or no Great Lakes fish (n = 419). The cohort was originally established in 1980-1982, and its characteristics have been described previously (9,11). The heavy fish eaters regularly consumed greater than 24 lb of sport-caught Lake Michigan fish per year, with consumption ranging from 24 to 270 lb/year (median = 38.5 lb/year). Subjects were recruited through visits to marinas, bait shops, and fishing clubs, and by referrals from other participants. The comparison group of people who consumed little or no Great Lakes fish was recruited through random-digit dialing in the communities where the fish eaters were recruited. They reported eating less than 6 lb of sport-caught fish per year.