Pb, PCB, and MeHg effects on an ERP go/no-go task Surkan et al. 2007), although the levels meas- ured at 11 years of age in this study are about half those seen at 5 years in a subsample of these participants (Boucher et al. 2009b). Five children had blood Pb concentrations above the 10-μg/dL threshold used by U .S. and Canadian public health agencies for evaluat- ing risk of Pb neurotoxicity and were there- fore referred to the appropriate public health authorities. Boys had higher blood Pb concen- trations at time of testing than did girls (3.4 vs. 2.0 gμ/dL, p < 0.001), which probably reflects their greater involvement in hunting-related activities. Cord PCB concentrations are about three times higher than in southern Québec (Ayotte et al. 2003) and similar to those in the Dutch PCB study (Longnecker et al. 2003). Cord Hg concentrations are about 20 times higher than in southern Québec (Muckle et al. 2001) and similar to those reported in children from the Faroe Islands (Debes et al. 2006). Associations among the concentrations of contaminants measured at birth and at time of testing are presented in Table 2. Pb, PCB-153, and Hg are moderately associated with each other, presumably because these substances are found at relatively high con- centrations in traditional Inuit food and fami- lies vary in the degree to which they consume traditional food. Behavioral performance. Values for mean RT and rates of correct responses on the go and no-go trials are presented in Table 1. Repeated-measures analysis of variance (ANOVA) showed that, as expected, partici- pants are more accurate on go than on no-go trials [F(1,195) = 655.4, p < 0.001]. Faster mean RT for go trials is associated with more accu- rate detection of go (r = –0.31, p < 0.001) and no-go (r = –0.19, p < 0.001) trials. Rates of correct responses for go trials are positively associated with rates of correct responses for no-go trials (r = 0.39, p < 0.001). Results from the regression analyses testing for associations between contaminant concen- trations and behavioral go/no-go performance are presented in Table 3. After control for confounding factors, higher Pb concentra- tions in cord blood are associated with fewer correct responses for both go and no-go trials. Higher blood Pb concentrations at time of testing are associated with an increased num- ber of false alarms in no-go trials, suggesting difficulty in inhibiting a prepotent response. This association falls just short of statistical significance when participants with blood Pb concentrations ≥ 5 μg/dL are excluded (n = 175; r = –0.18, p = 0.02; standard- ized β = –0.14, p = 0.078). Current plasma PCB-153 concentrations are associated with slower responses to go trials. PCB-153 con- centrations in cord plasma and Hg concentra- tions in cord and child blood samples were not associated with any of the behavioral measures after statistical control for confounding vari- ables (all p-values > 0.10). Figure 1 illustrates mean performance per quartile of exposure on each outcome significantly associated with a contaminant. Postnatal Pb and PCB-153 effects seem linear, whereas the adverse effects of prenatal Pb are mainly observed in the highest-exposed children. Testing for interactions revealed inter- action effects for cord Pb with both cord PCB and cord Hg for three behavioral mea- sures: incorrect no-go RT (standardized β: Pb × PCB = 0.14, p = 0.05; Pb × Hg = 0.12, p = 0.10 percent correct go (standardized β: Pb × PCB = –0.17, p = 0.04; Pb × Hg = –0.15, p = 0.07), and percent correct no-go trials (standardized β: Pb × PCB = –0.11, p = 0.12; Pb × Hg = –0.18, p = 0.01). Although not all these interactions reached conventional lev- els of statistical significance, the stratification analyses showed that the effects of cord Pb were seen primarily in the children with higher prenatal PCB and/or Hg exposures, indicating that the effects of prenatal Pb exposure were intensified by heavier PCB and Hg exposures. Stimulus-locked ERPs. In repeated- measures ANOVAs with condition (go vs. no-go) as a within-subject variable, P3 amplitude at parietal electrode (Pz) was sig- nificantly larger for no-go than for go trials [10.1 vs. 5.0 Vμ; F(1,192) = 119.7, p < 0.001], reflecting the additional resources needed to inhibit a prepotent response. No condition effect was found for N2 [frontal electrode (Fz)] latency (go: 375.9 msec; no-go: 370.7 msec) and amplitude (go: –7.4 μV; no-go: –7.8 Vμ; p-values > 0.20). Slower N2 latency was associated with slower mean hit RT (go N2: r = 0.35, p < 0.001; no-go N2: r = 0.30, p < 0.001) and with lower percent correct go trials (go N2: r = –0.23, p = 0.001; no-go N2: r = –0.30, p < 0.001). Greater P3 ampli- tude was significantly associated with greater percent correct go trials (go P3: r = 0.21, Table 3. Associations between contaminants and behavioral performance in the go/no-go task (n = 196). Behavioral outcome Mean RT, correct go trials Mean RT, incorrect no-go trials Percent correct go Percent correct no-go Pb Cord blood r β 0.06 –0.05a,b,c,d,e,f 0.14# 0.10a,b,d,g,h –0.12# –0.21**h,k,l –0.16** –0.17**b,d Current blood r β –0.01 0.03a,b,c,d,f 0.01 0.03a,b,d,g –0.11 –0.12k,l –0.20* –0.16**b,m PCB-153 Cord plasma r β 0.15** 0.04b,c,e,f 0.16** 0.07b,g,h,i –0.01 0.03h,i,k,l 0.05 0.06b,i,k,m,n,o Current plasma r β 0.17** 0.18**b,c,e,f 0.17** 0.06b,g,i –0.06 –0.01a,h,i,k,l –0.12 –0.06b,i,k,n,o Cord blood r β 0.13# 0.04a,b,c,d,f 0.10 0.03a,b,d,h,i,j –0.03 0.06a,h,k,i,l –0.06 0.07b,d,i,m,n Hg Current blood r β 0.15** 0.10a,b,c,d,f 0.20* 0.11a,b,d,h –0.11 –0.02a,h,i,l –0.07 –0.03b,i,k,m,o Values are Pearson correlation (r) and standardized regression (β) coefficients from multiple regression analyses. Superscripts (a–o) indicate control variables included in the final model for each of the regression analyses. aChild age. bChild sex. cAdoption status. dChild PCB-153. eCord Hg. fChild DHA. gChild Hg. hCord DHA. iCord Pb. jCord PCB-153. kTime at assessment. lMaternal marijuana during preg- nancy. mBreast-feeding duration. nTransported from a remote village. oChild Pb. *p < 0.01. **p < 0.05. #p < 0.10. 100 ) % ( s l ira 90 t o g t c e rr 80 o C 70 80 ) % ( s ila 70 r t o g - tno 60 c e r r o C 50 90 ) % l(s 80 a i r t go 70 - o n tec 60 r r o C 50 560 ) s m (e520 m i t n tico480 a e r t i hn440 a e M 400 0.8–2.5 2.5–3.7 3.7–5.6 5.6–20.9 Cord blood Pb (µg/dL) 0.8–2.5 2.5–3.7 3.7–5.6 5.6–20.9 Cord blood Pb (µg/dL) 0.4–1.3 1.3–2.0 2.0–2.9 2.9–12.8 11-year blood Pb (µg/dL) 3.5–26 26–46 46–97 97–431 11-year plasma PCB-153 (µg/kg fat) Figure 1. Mean ± SD behavioral performance in the go/no-go task according to quartiles of exposure: (A,B) cord blood Pb, (C) 11-year blood Pb, and (D) 11-year plasma PCB-153. Outcome measures are adjusted for the potential confounders listed in Table 3. Environmental Health Perspectives • volume 120 | number 4 | April 2012 611