Polychlorinated biphenyls (PCBs) and neurological development in children: a systematic review

Prenatal exposures to persistent organic pollutants as measured in cord blood and meconium from three localities of Zhejiang, China

Prenatal exposures to persistent organic pollutants were assessed using the levels of PCBs and organochlorine pesticides (OCPs) measured in cord blood and meconium samples from Luqiao and two other localities of the Zhejiang province in China. Luqiao is a town with the largest site for disassembly of PCB-containing obsolete transformers and electrical waste in China. The other two localities Pingqiao (100 km NW of Luqiao) and Lin'an (500 km NW of Luqiao) are towns without known electronic or electrical waste sites. A total of 23 PCB congeners (including 12 dioxin-like) and 6 OCPs were measured using the traditional GC-muECD technique. Micro-EROD bioassay was additionally used to measure TCDD-based TEQ levels of the 12 dioxin-like PCBs. Significant correlations were found between the TEQs measured by the two methods, supporting the application of micro-EROD as a practical tool for complementing the chemical analysis. The data showed that beta-HCH, p,p'-DDE, and 6 PCB congeners (101, 138, 153, 180, 183, and 187) were the predominant pollutants, with PCB138 being the best indicator (predictor) for total PCB levels. Cord blood and meconium from Luqiao have higher levels of PCBs than those from the other two localities, suggesting that a disassembly site for electronic and electric waste would provide an environment for greater exposure to these chemicals. The cord blood or meconium levels of beta-HCH, though likewise considerably high, were comparable in the three localities. Similar findings were observed for p,p'-DDE. Pollution by these OCPs might have come from past use of agricultural pesticides in the three localities.

Effects of polychlorinated biphenyls on maternal odor conditioning in rat pups

Polychlorinated biphenyls (PCBs) are pervasive environmental contaminants that can have damaging effects on physiologic, motoric and cognitive function. Results from studies on PCBs and behavior have shown that exposure can alter learning and memory processes and that these shifts in cognitive abilities can be related to changes in hormonal and neural function. Little experimentation has been done on the impact of exposure to PCBs on social and emotional development. Previous work has shown that exposure to PCBs in children can alter play behavior. Importantly, exposure to PCBs has been found to change aspects of maternal-offspring interactions in rodents. The present study examined the impact of PCBs on maternal odor conditioning in rat pups 12-14 days of age. A modified version of the conditioned place preference paradigm was used that incorporated a maternal-associated odor cue (lemon scent) as the conditioned stimulus. PCBs significantly depressed the preference for the maternal-associated cue but did not impair discrimination for a novel odor. These effects could arise due to changes in the social dynamics between the dam and offspring after co-exposure to PCBs. For example, dams exposed to PCBs during gestation have been found to show elevated grooming directed towards pups exposed to PCBs. This change in maternal care can have dramatic effects on behavioral and hormonal systems in the developing rat pup. In conclusion, perinatal PCBs alter important social behaviors of both the mother and pup, and these alterations could have long-lasting effects on behavioral, cognitive and emotional development.

Epidemiology and Etiology of Mental Retardation

Mental retardation (MR) is a manifestation of a heterogeneous set of impairments and conditions that result in cognitive limitation. It is a condition of medical, educational, and social importance. Physicians identify profound, severe, and moderate MR but rarely diagnose mild MR unless it is associated with a genetic or medical syndrome. From a medical perspective, the quest for etiology and the possibility of medical or surgical intervention to minimize deterioration are paramount. Educators, on the other hand are less concerned with causation than with academic achievement and school success. The majority of cases of mild MR is identified in school settings. Finally, the public uses the label to describe poor adaptive skills. Adults with MR who hold jobs, live independently, and participate in society are not always described as having MR. Thus some individuals characterized in childhood or adolescence as having mild MR become indistinguishable from the general population in adulthood.

Environmental hazards: evidence for effects on child health

The human fetus, child, and adult may experience adverse health outcomes from parental or childhood exposures to environmental toxicants. The fetus and infant are especially vulnerable to toxicants that disrupt developmental processes during relatively narrow time windows. This review summarizes knowledge of associations between child health and development outcomes and environmental exposures, including lead, methylmercury, polychlorinated biphenyls (PCBs), dioxins and related polyhalogenated aromatic hydrocarbons (PHAHs), certain pesticides, environmental tobacco smoke (ETS), aeroallergens, ambient air toxicants (especially particulate matter [PM] and ozone), chlorination disinfection by-products (DBPs), sunlight, power-frequency magnetic fields, radiofrequency (RF) radiation, residential proximity to hazardous waste disposal sites, and solvents. The adverse health effects linked to such exposures include fetal death, birth defects, being small for gestational age (SGA), preterm birth, clinically overt cognitive, neurologic, and behavioral abnormalities, subtle neuropsychologic deficits, childhood cancer, asthma, other respiratory diseases, and acute poisoning. Some environmental toxicants, notably lead, ionizing radiation, ETS, and certain ambient air toxicants, produce adverse health effects at relatively low exposure levels during fetal or child developmental time windows. For the many associations supported by limited or inadequate epidemiologic evidence, major sources of uncertainty include the limited number of studies conducted on specific exposure-outcome relationships and methodologic limitations. The latter include (1) crude exposure indices, (2) limited range of exposure levels, (3) small sample sizes, and (4) limited knowledge and control of potential confounders. Important knowledge gaps include the role of preconceptual paternal exposures, a topic much less studied than maternal or childhood exposures. Large longitudinal studies beginning before or during early pregnancy are urgently needed to accurately measure and assess the relative importance of parental and childhood exposures and evaluate relatively subtle health outcomes such as neuropsychologic and other functional deficits. Large case-control studies are also needed to assess the role of environmental exposures and their interactions with genetic factors in relatively uncommon outcomes such as specific types of birth defects and childhood cancers. There is also an urgent need to accelerate development and use of biomarkers of exposure and genetic susceptibility in epidemiologic studies. This review supports the priority assigned by international agencies to relationships between child health and air quality (indoor and outdoor), lead, pesticides, water contaminants, and ETS. To adequately address such priorities, governments and agencies must strengthen environmental health research capacities and adopt policies to reduce parental and childhood exposures to proven and emerging environmental threats.

Cell death mechanisms in AtT20 pituitary cells exposed to polychlorinated biphenyls (PCB 126 and PCB 153) and methylmercury

Polychlorinated biphenyls (PCBs) are persistent food contaminants that can have adverse effects on the endocrine and nervous systems, including the pituitary. In the present study, we have investigated cell death in the AtT20 pituitary cell line after exposure to coplanar PCB 126 and non-coplanar PCB 153. In addition, co-exposure to the PCBs and another neurotoxic food contaminant, methylmercury (MeHg), was studied to test possible interactive effects. Our results show that mainly necrosis is induced after exposure to the selected toxicants. Simultaneous exposure to moderately toxic doses of PCBs and MeHg resulted in additive or slightly synergistic effects on the induction of cell death. Furthermore, our data suggest that both PCB congeners trigger cell death in AtT20 cells via activation of calcium regulated calpains and lysosomal cathepsins, possibly through disruption of mitochondrial function and intracellular calcium signaling. However, caspase-activity appears not to be critical for PCB induced cell death in these cells. Presence of reactive oxygen species (ROS) and protective effects of pre-treatment with antioxidants were only found after MeHg exposure, suggesting that oxidative stress plays a major role in MeHg but not PCB toxicity in this experimental model.

Persistent organic pollutants and adverse health effects in humans

Persistent organic pollutants (POPs) are synthetic chemicals that have an intrinsic resistance to natural degradation processes, and are therefore environmentally persistent. The introduction of POPs into the environment from anthropogenic activities resulted in their widespread dispersal and accumulation in soils and water bodies, as well as in human and ecological food chains, where they are known to induce toxic effects. Due to their ubiquity in the environment and lipophilic properties, there is mounting concern over the potential risks of human exposure to POPs. This has led to the establishment of monitoring programs worldwide to determine prevailing levels of POPs in the population and to investigate the adverse health risks associated with background exposure. This article reviews the state of knowledge regarding residual levels of POPs in human adipose tissue worldwide, and highlights research data for POPs in the environment and human maternal adipose tissue in Singapore. Although concentrations are comparable to those observed elsewhere, longer term monitoring of a larger cross section of the population is warranted in order to establish temporal trends and potential risks to human health.

The effects of PCBs and dioxins on child health

BACKGROUND/EXPOSURE: Dioxins and PCBs are highly persistent and highly toxic environmental pollutants which at present are derived mainly from waste incineration and food contamination. They are widespread in nature and pollute human food, including breast milk so that basically all children in Europe are exposed to measurable levels. RESULTS/TOXICITY IN CHILDREN: The toxicity of dioxins and PCBs are well described both from animal studies and from a number of human epidemiological studies including several large cohort studies. Especially developmental exposure has been shown to affect endocrine and cognitive systems negatively. Measurable outcomes include reduced IQ and changed behaviour. Foetotoxic effects with reduced birth weight and increased congenital anomalies such as cleft lip have also been described. Exposure to PCBs and dioxins must be considered also in the context of multiple exposure to several toxins simultaneously or sequentially. CONCLUSION/SUGGESTED ACTION: Some measures aimed at reducing exposure to dioxins have been partly successful in that the dioxin content of breast milk is going down. However, further steps to reduce exposure must be taken. We suggest legislative measures for reducing the re-entry of especially PCBs from waste into the environment. Individual pre-conception counselling is recommended in order to reduce developmental exposure and its consequences. Biomonitoring of the substances themselves in breast milk and foods is recommended as well as monitoring possible endocrine effects.

Efficient testing strategies for evaluation of xenobiotics with neuroendocrine activity

Maturation of neuroendocrine regulations is an extremely complex process made up of several stages, that can be permanently affected by any exogenous substances able to interfere with the hormonal signalling at various levels. The Endocrine Disrupting Chemicals (EDCs) are a heterogeneous group of xenobiotics with potential endocrine activities which have been identified as priority risk factors in toxicological research. The present review is aimed at suggesting a number of endocrine and behavioural endpoints to be used in experimental studies to: (i) characterize more thoroughly the functional effects of developmental exposure to agents known to act as endocrine disruptors and (ii) unmask possible interferences with the maturation of the hypothalamus-hypophysis-gonad/thyroid (HHG/Th) axis by different class of xenobiotics not considered as EDCs. A combined testing strategy, considering both markers of endocrine/hormonal maturation and behavioural endpoints under hormonal control in laboratory rodents, may evidence even subtle perturbations of the neuroendocrine homeostasis, that often go undetected.

Measurement of organochlorines in commercial over-the-counter fish oil preparations: implications for dietary and therapeutic recommendations for omega-3 fatty acids and a review of the literature

CONTEXT

The consumption of fish high in omega-3 fatty acids is advocated by the American Heart Association to decrease the risk of coronary artery disease. However, fish contain environmental toxins such as mercury, polychlorinated biphenyls, and organochlorine pesticides, which may negate the beneficial cardiovascular effects of fish meals. Toxin levels vary depending on both the fish source and the specific toxin, and neither farm-raised nor wild fish are toxin free. Fish oil supplements also prevent the progression of coronary artery disease and reduce cardiovascular mortality. However, only sparse data exist on the level of toxins in fish oil. In a previous study we showed that the amount of mercury in 5 over-the-counter brands of fish oil was negligible.

OBJECTIVE

To determine the concentrations of polychlorinated biphenyls and other organochlorines in 5 over-the-counter preparations of fish oil.

DESIGN

The contents of 5 commercial fish oil brands were sent for organochlorine analysis.

RESULTS

The levels of polychlorinated biphenyls and organochlorines were all below the detectable limit.

CONCLUSIONS

Fish oil supplements are more healthful than the consumption of fish high in organochlorines. Fish oils provide the benefits of omega-3 fatty acids without the risk of toxicity. In addition, fish oil supplements have been helpful in a variety of diseases, including bipolar disorder and depression.

Exposure to organochlorine compounds and effects on ovarian function

BACKGROUND

Some chemicals appear to have hormonally active properties in animals, but data in humans are sparse. Therefore, we examined ovarian function in relation to organochlorine compound levels.

METHODS

During 1997-1999, 50 Southeast Asian immigrant women of reproductive age collected urine samples daily. These samples were assayed for metabolites of estrogen and progesterone, and the women's menstrual cycle parameters were assessed. Organochlorine compounds (including DDT, its metabolite DDE, and 10 polychlorinated biphenyl [PCB] congeners) were measured in serum.

RESULTS

All samples had detectable DDT and DDE, with mean levels higher than typical U.S. populations. Mean cycle length was approximately 4 days shorter at the highest quartile concentration of DDT or DDE compared with the lowest. After adjustment for lipid levels, age, parity, and tubal ligation, and exclusion of a particularly long cycle, the decrements were attenuated to less than 1 day, with wide confidence intervals (CIs). The adjusted mean luteal phase length was shorter by approximately 1.5 days at the highest quartile of DDT (95% CI = -2.6 to -0.30) or DDE (-2.6 to -0.20). With each doubling of the DDE level, cycle length decreased 1.1 day (-2.4 to 0.23) and luteal phase length decreased 0.6 days (-1.1 to -0.2). Progesterone metabolite levels during the luteal phase were consistently decreased with higher DDE concentration. PCB levels were not generally associated with cycle length or hormone parameters after adjustment, and they did not alter the DDE associations when included in the same models.

CONCLUSIONS

This study indicates a potential effect of DDE on ovarian function, which may influence other end points such as fertility, pregnancy, and reproductive cancers.

In utero exposure to polychlorinated biphenyls and sensorineural hearing loss in 8-year-old children

Early-life exposure to polychlorinated biphenyls (PCBs), a ubiquitous environmental contaminant, increases the hearing threshold at selected frequencies in rats. Among humans from the Faroe Islands with unusually high early-life PCB exposure, exposure was directly associated with increased hearing thresholds at two frequencies, although the deficits were present in the left ear but not the right. We examined PCB levels in maternal pregnancy serum in relation with audiometrically determined hearing thresholds among offspring when they were of school age. Complete data were available for 195 children with sensorineural hearing loss (SNHL) and 615 children selected at random, all of whom were born in 1959-1966 in the Collaborative Perinatal Project (CPP) U.S. cohort. The median exposure among those selected at random, as reflected by the mother's third trimester serum total PCB concentration, was 2.8 microg/l, about twofold higher than recent background levels in the United States. Based on the average hearing threshold across the frequencies essential for speech recognition in the "worst ear," the maternal serum PCB level was unrelated to the adjusted odds of SNHL or to adjusted mean hearing threshold. Overall, an adverse effect of early-life, background-level PCB exposure on SNHL was not supported by these data.

Assessment of pre- and postnatal exposure to polychlorinated biphenyls: lessons from the Inuit Cohort Study

Polychlorinated biphenyls (PCBs) are food-chain contaminants that have been shown to induce adverse developmental effects in humans. In the course of an epidemiologic study established to investigate neurodevelopmental deficits induced by environmental PCB exposure in the Inuit population of northern Québec (Nunavik, Canada), we compared three biomarkers of prenatal exposure and models to predict PCB plasma concentration at 6 months postpartum. Concentrations of 14 PCB congeners were measured by high-resolution gas chromatography with electron capture detection in lipids extracted from maternal plasma, cord plasma, breast milk (collected at approximately 1 month postpartum), and 6-month-old infant plasma samples. Similar congener profiles were observed in all biologic samples, and PCB-153, the most abundant and persistent PCB congener, was strongly correlated with other frequently detected PCB congeners in all biologic media. When expressed on a lipid basis, maternal plasma, cord plasma, and milk concentrations of this congener were strongly intercorrelated, indicating that PCB concentration in any of these biologic media is a good indicator of prenatal exposure to PCBs. A multivariate model that included maternal PCB-153 plasma lipid concentration, breast-feeding duration, and the sum of two skin-fold thicknesses (an index of infant body fat mass) explained 72% of PCB-153 plasma concentration variance at 6 months postpartum (p < 0.001). By contrast, based on the product of breast-feeding duration times the concentration of PCBs in plasma lipids, which was used as an index of postnatal PCB exposure in several studies, only 36% of infant plasma concentration was explained.

Breastfeeding, exposure to organochlorine compounds, and neurodevelopment in infants

OBJECTIVE

Exposure to organochlorine compounds (OCs) occurs both in utero and through breastfeeding. Levels of hexachlorobenzene (HCB) found in the cord serum of newborns from a population located in the vicinity of an electrochemical factory in Spain were among the highest ever reported. We studied the association between exposure to OCs and breastfeeding on neurodevelopment in the 1-year-old infants of this population.

METHODS

A birth cohort including 92 mother-infant pairs was recruited between 1997 and 1999 in 5 neighboring villages (84% of possible recruits). The mental and psychomotor development of each infant was assessed at 13 months using the Bayley and the Griffiths Scales of Infant Development. OCs were measured in cord serum.

RESULTS

Dichlorodiphenyl dichloroethylene (p,p'DDE) cord serum levels were negatively associated with both mental and psychomotor development. For each doubling of a dose of p,p'DDE, we found a resultant decrease of 3.50 points (standard error: 1.39) on the mental scale and 4.01 points (standard error: 1.37) on the psychomotor scale. Exposure to polychlorinated biphenyls was only marginally associated with psychomotor development. Prenatal exposure to HCB had no effect on child neurodevelopment. Long-term breastfeeding was associated with better performance on both the mental and motor scales. Short-term breastfed infants with higher p,p'DDE levels in cord serum were associated with the lowest scores on both the mental and the psychomotor scales.

CONCLUSIONS

Prenatal exposure to p,p'DDE was associated with a delay in mental and psychomotor development at 13 months. No association was found for exposure to HCB. Long-term breastfeeding was found to be beneficial to neurodevelopment, potentially counterbalancing the impact of exposure to these chemicals through breast milk.

Organochlorines in Swedish women: determinants of serum concentrations

We studied associations between lifestyle/medical factors and lipid-adjusted serum concentrations of seven polychlorinated biphenyl (PCB) congeners and five chlorinated pesticides/metabolites among 205 Swedish women (54-75 years old). Serum concentrations were significantly associated with age, body mass index, body weight change, diabetes mellitus, consumption of fatty fish, and place of residence. The findings suggest that lifestyle/medical factors may confound results in epidemiologic studies when they are related to both serum concentrations and disease. Moreover, disease itself may influence serum concentrations of some organochlorines, as indicated by the negative associations between recent weight change and serum concentrations of some PCB congeners, p,p -dichlorodiphenyldichloroethylene (DDE), and hexachlorobenzene (HCB) and the positive association between diabetes mellitus and HCB concentrations. Age was the only determinant that showed a consistent association with all compounds studied (positive); otherwise associations with single determinants varied among compounds even within the PCB group. This shows that the studied organochlorines should not be treated as a homogeneous group of compounds in epidemiologic studies.

Human Exposure to Polychlorinated Biphenyls and Health Effects

Polychlorinated biphenyls (PCBs) are a mixture of chemicals. Some congeners of the mixture are highly persistent both in the environment and in humans. Although PCBs have not been used commercially since about 1977 in the US, they can still be detected in human blood and tissues in this country. PCB levels are declining and are often no longer detectable in younger people. A cursory review of recent animal studies is provided. Studies to determine whether PCBs cause cancer in humans, neurobehavioural effects, abnormal thyroid and immune function in children and low birth weight are discussed in more detail. These studies are inconclusive and do not provide clinical evidence that PCBs at levels encountered with human exposure produce adverse health effects. The differences in PCB blood or tissue concentrations between controls and cases, or between the upper and lower end of various environmentally exposed groups of children or adults, are small. Although some effects are statistically significantly different, they do not appear to be biologically significant. Many studies on the effects of PCBs are difficult to interpret because the range of normal values for clinical and neurobehavioural tests are not provided or appropriately considered, there was no, or inadequate, control for potential confounders. In occupational mortality studies, exposures were much higher. In some studies, various specific cancers were elevated. However, these appear to be chance observations resulting from multiple comparisons since the increase of specific cancers was not consistent between studies and was no longer present in some cohorts when studies were repeated at a later date with longer follow-up. Overall, the data fail to demonstrate conclusive adverse health effects of PCBs at concentrations encountered with human exposures.

Environmental factors associated with a spectrum of neurodevelopmental deficits

A number of environmental agents have been shown to demonstrate neurotoxic effects either in human or laboratory animal studies. Critical windows of vulnerability to the effects of these agents occur both pre- and postnatally. The nervous system is relatively unique in that different parts are responsible for different functional domains, and these develop at different times (e.g., motor control, sensory, intelligence and attention). In addition, the many cell types in the brain have different windows of vulnerability with varying sensitivities to environmental agents. This review focuses on two environmental agents, lead and methylmercury, to illustrate the neurobehavioral and cognitive effects that can result from early life exposures. Special attention is paid to distinguishing between the effects detected following episodes of poisoning and those detected following lower dose exposures. Perinatal and childhood exposure to high doses of lead results in encephalopathy and convulsions. Lower-dose lead exposures have been associated with impairment in intellectual function and attention. At high levels of prenatal exposure, methylmercury produces mental retardation, cerebral palsy and visual and auditory deficits in children of exposed mothers. At lower levels of methylmercury exposure, the effects in children have been more subtle. Other environmental neurotoxicants that have been shown to produce developmental neurotoxicity include polychlorinated biphenyls (PCBs), dioxins, pesticides, ionizing radiation, environmental tobacco smoke, and maternal use of alcohol, tobacco, marijuana and cocaine. Exposure to environmental agents with neurotoxic effects can result in a spectrum of adverse outcomes from severe mental retardation and disability to more subtle changes in function depending on the timing and dose of the chemical agent.

Identifying and managing adverse environmental health effects: 5. Persistent organic pollutants

Concern and awareness is growing about the health effects of exposures to environmental contaminants, including those found in food. Most primary care physicians lack knowledge and training in the clinical recognition and management of the health effects of environmental exposures. We have found that the use of a simple history-taking tool - the CH2OPD2 mnemonic (Community, Home, Hobbies, Occupation, Personal habits, Diet and Drugs) - can help physicians identify patients at risk of such health effects. We present an illustrative case of a mother who is concerned about eating fish and wild game because her 7-year-old son has been found to have learning difficulties and she is planning another pregnancy. Potential exposures to persistent organic pollutants (POPs) and mercury are considered. The neurodevelopmental effects of POPs on the fetus are reviewed. We provide advice to limit a patient's exposure to these contaminants and discuss the relevance of these exposures to the learning difficulties of the 7-year-old child and to the planning of future pregnancies.