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Paul W. Stewart,¹ David M. Sargent,¹ Jacqueline Reihman,¹ Brooks B. Gump,¹ Edward Lonky,¹ Thomas Darvill,¹ Heraline Hicks,² and James Pagano³

¹Department of Psychology, State University of New York at Oswego, Oswego, New York, USA; ²Agency for Toxic Substances and Disease Registry, Division of Environmental Medicine, Atlanta, Georgia, USA; ³Environmental Research Center, State University of New York at Oswego, Oswego, New York, USA

Abstract
Background: Animal studies have shown that exposure to common, low-level environmental contaminants [e.g., polychlorinated biphenyls (PCBs) , lead] causes excessive and inappropriate responding on intermittent reinforcement schedules. The Differential Reinforcement of Low Rates task (DRL) has been shown to be especially sensitive to low-level PCB exposure in monkeys.

Objectives: We investigated the relationships between prenatal PCB and postnatal Pb exposure performance on a DRL schedule in children. We predicted that a) prenatal PCB exposure would reduce interresponse times (IRTs) and reinforcements earned, and b) postnatal Pb exposure would reduce IRTs and reinforcements earned.

Methods: We tested 167 children on a DRL20 (20 sec) reinforcement schedule, and recorded IRTs and the number of reinforced responses across the session. We measured prenatal PCB exposure (cord blood) , methylmercury (MeHg) (maternal hair) , and postnatal Pb exposure (venous blood) , and > 50 potentially confounding variables.

Results: Results indicated impaired performance in children exposed to PCBs, MeHg, and Pb. Children prenatally exposed to PCBs responded excessively, with significantly lower IRTs and fewer reinforcers earned across the session. In addition, exposure to either MeHg or Pb predicted statistically significant impairments of a similar magnitude to those for PCBs, and the associated impairments of all three contaminants (PCB, MeHg, and Pb) were statistically independent of one another.

Conclusions: These results, taken with animal literature, argue the high sensitivity of DRL performance to low-level PCB, MeHg, and Pb exposure. Future research should employ behavioral tasks in children, such as DRL, that have been demonstrably sensitive to low-level PCB, MeHg, and Pb exposure in animals.

Key words: differential reinforcement of low rates, DRL, fixed interval, inhibition, PCBs, polychlorinated biphenyls. Environ Health Perspect 114: 1923–1929 (2006) . doi:10.1289/ehp.9216 available via http://dx.doi.org/ [Online 18 August 2006]

Address correspondence to P.W. Stewart, 304 Mahar Hall, State University of New York at Oswego, Oswego, NY 13126 USA. Telephone: (315) 312-5437. Fax: (315) 312-6274. E-mail: pstewar1@oswego.edu

The authors thank P. West, C. Hosley, and S. Fitzgerald for their efforts in collecting these data.

This research was supported by Agency for Toxic Substances and Disease Registry grant H75-ATH298362-11 and National Institutes of Environmental Health Sciences grant ES09815-04.

The authors declare they have no competing financial interests.

Received 30 March 2006 ; accepted 17 August 2006.

Correction

In Table 1, some of the SES correlations for 1 year and 9 years were incorrectly noted as negative in the original manuscript published online. All scores were positive, and have been corrected here.