Effects of Cadmium, Lead, Mercury, and Arsenic in Children
Effects of Cadmium, Lead, Mercury, and Arsenic in Children
Lead, cadmium, mercury, and arsenic are common environmental pollutants in industrialized countries, but their combined impact on children's health is little known. We studied their effects on two main targets, the renal and dopaminergic systems, in > 800 children during a cross-sectional European survey. Control and exposed children were recruited from those living around historical nonferrous smelters in France, the Czech Republic, and Poland. Children provided blood and urine samples for the determination of the metals and sensitive renal or neurologic biomarkers. Serum concentrations of creatinine, cystatin C, and β2-microglobulin were negatively correlated with blood lead levels (PbB), suggesting an early renal hyperfiltration that averaged 7% in the upper quartile of PbB levels (> 55 µg/L; mean, 78.4 µg/L). The urinary excretion of retinol-binding protein, Clara cell protein, and N-acetyl-β-d-glucosaminidase was associated mainly with cadmium levels in blood or urine and with urinary mercury. All four metals influenced the dopaminergic markers serum prolactin and urinary homovanillic acid, with complex interactions brought to light. Heavy metals polluting the environment can cause subtle effects on children's renal and dopaminergic systems without clear evidence of a threshold, which reinforces the need to control and regulate potential sources of contamination by heavy metals.
Environmental pollution of industrialized countries by heavy metals such as lead, cadmium, mercury, and the metalloid arsenic is largely the consequence of past emissions by nonferrous industries. Although stringent measures and controls have been put into place during the last decades, high levels of these pollutants still persist in the soils and sediments--and therefore also in the food chain--with possible consequences of chronic environmental exposure of the populations living in those areas. Moreover, natural contamination such as geologic arsenic or lifestyle-related factors such as the inorganic mercury in dental amalgam can further contribute to increase the burden of human exposure to these toxicants.
Most of our knowledge concerning the health effects of toxic metals largely stems from studies conducted on populations with relatively high exposure usually to individual metals in industry or in heavily polluted environments. Very few studies have addressed the possible effects of chronic low environmental exposure to mixtures of these metals, particularly with regard to their possible interactions, although this is precisely the situation most commonly encountered by the general population of industrialized countries. Furthermore, there is a definite paucity of data concerning children, a specific cause for concern because children are known to absorb metals more readily than adults and are particularly sensitive for biologic and developmental reasons (Fels et al. 1998).
Among possible target organs of heavy metals, the kidney and central nervous system appear to be the most sensitive ones. Inorganic heavy metals have been known for a long time to be nephrotoxic at relatively high levels of exposure, with numerous reports of tubulointerstitial nephritis possibly leading to renal failure, in most cases linked to high occupational or environmental exposure (Fowler 1996). Early signs of renal dysfunction can, however, be found with exposure to low environmental levels of these heavy metals, consisting in decreased glomerular filtration rate (GFR) (lead) or increased urinary loss of tubular enzymes (cadmium). These effects have been described mainly in adults, but certain reports have also shown them to occur in children (Bernard et al. 1995; Verberk et al. 1996). Neurotoxic effects of heavy metals are also well documented, especially for mercury and lead, with numerous reports of neurobehavioral changes after occupational exposure and of developmental effects in children with pre- or early postnatal exposure (Davidson et al. 2004; Lidsky and Schneider 2003). However, experimental studies suggest that other metals such as cadmium and arsenic could also interfere with the nervous system and that all four metals may influence the dopaminergic system in different ways (Lafuente et al. 2003b; Pohl et al. 2003). There is, however, a need to elucidate which exposure levels are likely to cause these biologic effects, particularly in children, and to what extent the four metals could interfere and interact in mixed exposures.
To address some of these issues, in the present study we focused on populations of children living in three separate European regions known for their historical levels of pollution in France, Poland, and the Czech Republic. The levels of exposure to cadmium, lead, mercury, and arsenic were determined in about 800 children together with a set of sensitive biomarkers of kidney function and of the dopaminergic system.
Lead, cadmium, mercury, and arsenic are common environmental pollutants in industrialized countries, but their combined impact on children's health is little known. We studied their effects on two main targets, the renal and dopaminergic systems, in > 800 children during a cross-sectional European survey. Control and exposed children were recruited from those living around historical nonferrous smelters in France, the Czech Republic, and Poland. Children provided blood and urine samples for the determination of the metals and sensitive renal or neurologic biomarkers. Serum concentrations of creatinine, cystatin C, and β2-microglobulin were negatively correlated with blood lead levels (PbB), suggesting an early renal hyperfiltration that averaged 7% in the upper quartile of PbB levels (> 55 µg/L; mean, 78.4 µg/L). The urinary excretion of retinol-binding protein, Clara cell protein, and N-acetyl-β-d-glucosaminidase was associated mainly with cadmium levels in blood or urine and with urinary mercury. All four metals influenced the dopaminergic markers serum prolactin and urinary homovanillic acid, with complex interactions brought to light. Heavy metals polluting the environment can cause subtle effects on children's renal and dopaminergic systems without clear evidence of a threshold, which reinforces the need to control and regulate potential sources of contamination by heavy metals.
Environmental pollution of industrialized countries by heavy metals such as lead, cadmium, mercury, and the metalloid arsenic is largely the consequence of past emissions by nonferrous industries. Although stringent measures and controls have been put into place during the last decades, high levels of these pollutants still persist in the soils and sediments--and therefore also in the food chain--with possible consequences of chronic environmental exposure of the populations living in those areas. Moreover, natural contamination such as geologic arsenic or lifestyle-related factors such as the inorganic mercury in dental amalgam can further contribute to increase the burden of human exposure to these toxicants.
Most of our knowledge concerning the health effects of toxic metals largely stems from studies conducted on populations with relatively high exposure usually to individual metals in industry or in heavily polluted environments. Very few studies have addressed the possible effects of chronic low environmental exposure to mixtures of these metals, particularly with regard to their possible interactions, although this is precisely the situation most commonly encountered by the general population of industrialized countries. Furthermore, there is a definite paucity of data concerning children, a specific cause for concern because children are known to absorb metals more readily than adults and are particularly sensitive for biologic and developmental reasons (Fels et al. 1998).
Among possible target organs of heavy metals, the kidney and central nervous system appear to be the most sensitive ones. Inorganic heavy metals have been known for a long time to be nephrotoxic at relatively high levels of exposure, with numerous reports of tubulointerstitial nephritis possibly leading to renal failure, in most cases linked to high occupational or environmental exposure (Fowler 1996). Early signs of renal dysfunction can, however, be found with exposure to low environmental levels of these heavy metals, consisting in decreased glomerular filtration rate (GFR) (lead) or increased urinary loss of tubular enzymes (cadmium). These effects have been described mainly in adults, but certain reports have also shown them to occur in children (Bernard et al. 1995; Verberk et al. 1996). Neurotoxic effects of heavy metals are also well documented, especially for mercury and lead, with numerous reports of neurobehavioral changes after occupational exposure and of developmental effects in children with pre- or early postnatal exposure (Davidson et al. 2004; Lidsky and Schneider 2003). However, experimental studies suggest that other metals such as cadmium and arsenic could also interfere with the nervous system and that all four metals may influence the dopaminergic system in different ways (Lafuente et al. 2003b; Pohl et al. 2003). There is, however, a need to elucidate which exposure levels are likely to cause these biologic effects, particularly in children, and to what extent the four metals could interfere and interact in mixed exposures.
To address some of these issues, in the present study we focused on populations of children living in three separate European regions known for their historical levels of pollution in France, Poland, and the Czech Republic. The levels of exposure to cadmium, lead, mercury, and arsenic were determined in about 800 children together with a set of sensitive biomarkers of kidney function and of the dopaminergic system.