Child neurodevelopment in a Bolivian mining city

Abstract

This study evaluates the neurodevelopment of children living near contaminated mining industries during their first year of life. Participants from the city of Oruro (Bolivia) were prospectively recruited during pregnancy. Follow-up occurred between May 2007 and November 2009. Information about the socioeconomic status and medical history of the pregnant women were collected using questionnaires. Neurodevelopment was evaluated for 246 children using the Bayley Scales of Infant Development (BSID) at 10.5–12.5 months of age. Exposure to trace elements (Pb, As, Cd, Sb, Cs, Zn, Fe, Cu, Se, Rb, and Sr) during prenatal life was evaluated by testing maternal blood concentrations before delivery. Almost all measured levels were lower than the control limits. The blood lead concentration of pregnant women was low, considering the contaminated environmental context. The geometric mean was 1.76 μg/dL (95% CI: 1.68–1.84), a level comparable with those observed in non-contaminated areas. The only element found to be relatively elevated was antimony, with a geometric mean of 1.03 μg/dL (95% CI: 0.96–1.11). Our results suggest that women from this mining area were not highly exposed. The Bayley Scales of Infant Development (BSID) did not reveal mental or psychomotor abnormalities. Surprisingly, at the observed low levels, lead was positively associated with the children's BSID performance.

Introduction

The Bolivian economy relies in part on the exploitation and exportation of natural resources such as tin, copper, and silver (Smolders et al., 2003, Van Damme et al., 2008). Most major Bolivian mining corporations are located near medium and large urban centers; these corporations offer very basic, if any, safety measures for both their workers and the citizens living in the vicinity of the mines. Although various contaminants affecting Bolivian urban populations have been described (Rojas and Vandecasteele, 2007), few studies have examined the environmental impact of the Bolivian mining industry. Children are particularly sensitive to environmental contaminants. For instance, several metals are related to impaired child neurodevelopment (Bellinger, 2008a, Bellinger, 2008b, Gilbert and Weiss, 2006, Jedrychowski et al., 2009, Shen et al., 1998, Téllez-Rojo et al., 2006).

Studies conducted in South America have described the significant impact of the mining industry on urban populations (Håkan Tarras-Wahlberg and Nguyen, 2008, Liu et al., 2005, Moreno et al., 2010). Studies in Peru have documented the harmful effects on children's health due to the considerable environmental contamination caused by mining and metallurgical industries (Astete et al., 2009, Conklin et al., 2007, Pebe et al., 2008). The flat highlands of Bolivia (known as Altiplano) are particularly rich in natural resources that are highly desirable in the global market, e.g. gold, silver, tin, copper, zinc, and antimony. These metals are associated with toxic elements such as lead, cadmium, and arsenic. Oruro (17°58′ S–67°06′ W) is an Altiplano ‘mining city’ located at an altitude of 3700 m.a.s.l. The presence of mining wastes, smelters, and ore dressing industries makes Oruro comparable to La Oroya (located in the central highlands of Peru), often cited for being one of the most contaminated cities in the world (Fraser, 2009, Fraser, 2006). Most of the 250,000 inhabitants of Oruro live, work, and interact in close proximity to the city mines. As a result, the majority of the population is exposed to polymetals on a daily basis—with minimal awareness of the potential adverse effects on health and particularly the potential deleterious effects on the developing human brain (Grandjean and Landrigan, 2006, Wigle et al., 2008). The Oruro population is relatively young, with 36% of the inhabitants under the age of 15. Women of child bearing age represent about 20% of the population (MEASURE, 2004).

Except for a brief period between the mid-1980s and the early 1990s, the Oruro San José mine has been exploited for more than 400 years. Since at least the 17th century, millions of tons of mining waste have been dumped in San José. Today, many homes have been built on the small hills around the mine. These hills are composed of mining waste material. Several studies have investigated the public health risks posed by water contamination from mines in the neighboring cities (PAADO, 2005). In March 2007, given the mining extraction and productivity record, local communities and other organizations directly affected by mining contaminants held a meeting in Oruro to condemn and confront the mining industry. In this context, the ToxBol pilot project collected and analyzed hair samples taken from children in local schools, as well as home dust samples. Both types of samples revealed a high environmental contamination index.

ToxBol (Toxicity in Bolivia) is a multidisciplinary research project with the objective to study the origin of polymetallic contamination in the Oruro environment and its impact on public health. The aim of the present study is to determine the association of polymetallic exposure and the mental and psychomotor development of one-year-old children whose mothers live in Oruro.