Environmental exposure to multiple chemical elements in Peruvian populations: a review of selected studies

Introduction

Most human diseases rely on laboratory confirmation to establish the presence of disease, but this may be an unmet expectation in environmental exposure assessments because there is currently a knowledge gap between data generated by scientific research and the practical applications of that knowledge to Public Health interventions.¹ Human exposure assessment to chemical elements is complex, and “the ability to measure chemicals in humans is far outpacing the ability to reliably interpret these data for Public Health purposes”.² Biomonitoring (measuring chemicals in human biological samples) can fail to provide information to support Public Health decisions, mostly because results can be difficult to interpret in proper context and the absence of relevant environmental legislation produces a dangerous oversight that is common to many developing countries.³ Regardless, data from human exposure to environmental contaminants is constantly produced, creating a need to assess relationships with potential adverse health impacts and identify potential sources and pathways.²

Human exposure to environmental chemical elements by air, dust, or water, is inherent to local mining or oil extractive activities, and is a major public health issue in Peru. Environmental and biological evaluations are constantly being carried out by both governmental and private institutions to assess human exposure to different chemical elements. There are plenty of isolated reports regarding exposure to certain heavy metals/metalloids (i.e., lead and mercury) in populations considered not to be occupationally exposed (i.e., children), at levels that would be considered a clinical emergency in other countries.^4–6 Suggested explanations for these apparent discrepancies in Peruvian children include genetic adaptation,⁷ physiological changes from living at high altitudes,⁸ and the interaction between chemicals inside the human body.⁹ These “grey literature” observational studies report high levels of heavy metals when compared to other countries, but are seldom included in the scientific literature. We summarize results from official reports of five evaluations performed in Peru by the Division of Laboratory Sciences (DLS) at the National Center for Environmental Health (NCEH) of the Centers for Disease Control and Prevention (CDC) of the United States and compare the results with national reports from other countries. The objective of the study is to identify valuable conclusions that can be drawn from CDC’s DLS analysis in Peru between 2005 and 2013.

Methods

Researchers at CDC’s DLS have been pioneers in developing laboratory techniques to measure a broad spectrum of chemical elements in human biological samples (biomonitoring),¹⁰ and their laboratories have international prestige and are considered “reference laboratories” by the World Health Organization.

Setting

All exposure assessments responded to community concerns about industrial contamination of natural resources (Figure 1). The city of La Oroya (3745 meters above sea level) includes one of the largest smelting facilities in the world. Three communities are within the area of influence of open pit mines: the province of Espinar (3929 m.a.s.l.), the town of Ayash (3503 m.a.s.l.) is downstream from a top-five world copper production mine, and the Andean capital of Cerro de Pasco (4330 m.a.s.l.) was built over an ancient Pre-Columbian silver mine. Huepethue (414 m.a.s.l.) is a modern day “boom town” in the rainforest where prospectors from all over the world arrive looking for gold in the Amazon riverbeds.

Figure 1. Case sampling locations in Peru.

Data analysis

The percentage of urine samples with a detectable concentration for each chemical element is presented in Figure 2 and geometric means for four elements are plotted in Figure 3. The National Health and Nutrition Examination Survey (NHANES) in the United States is designed to assess the health and nutritional well-being of children and adults using a representative sample (noninstitutionalized, civilian) of the entire population.¹⁶ Findings from the NHANES survey are used to determine the prevalence and risk factors of major diseases and are also the basis for national standards.¹⁷ Data from national surveys help develop public health policy, health programs and services, and expand the scientific knowledge on a population’s health,^18,19 but biomarker measures from NHANES are not useful for demonstrating temporality, nor are they useful for evaluating causation or reverse causation.²⁰

Figure 2. Percentage of participants with detectable levels of 13 and 17 elements in Spot Urine Samples at 4 locations in Peru, 2006-2013.

Note: Strontium, manganese, mercury, and tin were only reported in 2 of the exposure assessments.

Figure 3. Geometric Means and Confidence Intervals for selected chemical elements in Spot Urine Samples in the United States, Canada and selected locations in Peru, 1999-2018.

Results

Five environmental exposure assessments analysed spot urine samples from the following study populations: 343 participants from La Oroya in 2005;¹¹ 253 participants from Ayash in 2006;¹² 354 participants from Cerro de Pasco in 2007;¹³ 98 participants from Huepethue in 2010;¹⁴ and 180 participants from Espinar in 2013¹⁵ (Figure 1 & Table 1).

Evidence of exposure – Qualitative analysis For this analysis, any “detectable” level (above the LOD) is considered evidence of “exposure”, regardless of the amount detected. The percentage of spot urine samples with evidence of exposure varied between locations (Figure 2, data not available for La Oroya). Six chemical elements (total arsenic, caesium, cobalt, molybdenum, lead and thallium) were detected in almost all samples tested (average over 98%), while two other elements (beryllium and platinum) were very seldom detected, <3% and <10% respectively. Other chemical elements like barium, cadmium and tungsten were reported (on average) to be present in over 90% of all samples, while antimony (range 51-96%) and uranium (range 41-83%) were variably prevalent in different locations. Exposure to antimony was more frequent (96%) in samples from participants in Cerro de Pasco, and less frequent (<65%) in other locations. Similarly, uranium was detected more frequently (between 68% and 83%) in 3 Andean locations (Ayash, Cerro de Pasco, and Espinar), but less frequently (41%) in urine samples from the rainforest town at Huepethue. Data for strontium, mercury, manganese, and tin was available for 2 of the 5 locations (Figure 2).

Comparison among populations – Quantitative analysis For this analysis, urine concentration geometric means were retrieved from official reports for selected chemical elements and compared to geometric means from nationally representative studies in the United States²⁸ and Canada,²⁹ that are also available in France.³⁰ The (not statistically valid) comparison was made for 3 of the 5 sites using geometric means and estimated 95th percentile in the United States. Chemical elements like total arsenic and lead appear to have a higher geometric mean in Peru when compared to national averages from the United States and Canada, but cadmium and mercury have a lower geometric mean in some locations in Peru (Figure 3).

Discussion

The health implications for environmental exposure vary among chemical elements and the sources of environmental contaminants vary by location. In Peru, total arsenic, caesium, cobalt, lead, molybdenum, and thallium are almost universally present in urine samples from all five locations. However, there are some key issues that must be considered before attempting to assess human impact from exposure to chemical elements: 1) these are complex/mixed exposures, 2) there is individual variability, and 3) the potential confounding factor from natural exposure.

Complex exposures People can be exposed to more than one chemical at the same time, and studies analysing only one chemical element at a time ignore the potential interactions between chemicals inside the human body. These interactions can range from synergy (a cooperation of two or more substances to produce a combined effect greater than the sum of their separate effects) to antagonism (a substance acts against or blocks the action of another substance). Much remains unknown about the health effects of these mixed interactions where several environmental toxics (including heavy metals, pesticides, and hydrocarbons), from different environmental sources (natural and/or artificial), and through different environmental exposure pathways (air, soil, water and food) can increase the risk of developing diseases. Few human exposure studies analyse multiple elements from a single biological sample, and even when they do, reference information regarding health effects may not be available for all detectable elements.

Conclusions

Some Peruvians are exposed to several chemicals. Biomonitoring alone does not explain at what time, dose, and for how long the exposure occurred, which is essential to estimate the health impact of the inadvertent exposure. Relevant reference levels should be developed for each exposed population. Meanwhile, biomonitoring studies can help prioritize Public Health strategies for different populations in Peru.