Mercury Exposure and Children's Health

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Abstract

Acute or chronic mercury exposure can cause adverse effects during any period of development. Mercury is a highly toxic element; there is no known safe level of exposure. Ideally, neither children nor adults should have any mercury in their bodies because it provides no physiological benefit. Prenatal and postnatal mercury exposures occur frequently in many different ways. Pediatricians, nurses, and other health care providers should understand the scope of mercury exposures and health problems among children and be prepared to handle mercury exposures in medical practice. Prevention is the key to reducing mercury poisoning. Mercury exists in different chemical forms: elemental (or metallic), inorganic, and organic (methylmercury and ethyl mercury). Mercury exposure can cause acute and chronic intoxication at low levels of exposure. Mercury is neuro-, nephro-, and immunotoxic. The development of the child in utero and early in life is at particular risk. Mercury is ubiquitous and persistent. Mercury is a global pollutant, bio-accumulating, mainly through the aquatic food chain, resulting in a serious health hazard for children. This article provides an extensive review of mercury exposure and children's health.

Introduction

Mercury is a silvery-white shiny heavy metal with unique chemical and physical properties. It has been used worldwide for many centuries for commercial and medicinal purposes.1, 2 Mercury is a persistent and globally cycling element. Mercury occurs not only anthropogenically but also naturally.3, 4 It has toxic properties and severely affects the environment and humans, especially developing fetuses and infants.3

There are 3 main forms of mercury that differ with respect to their toxicokinetics regarding absorption, distribution, and accumulation in the human body; related health outcomes; and the extent of cycling in the environment. Elemental mercury is liquid at room temperature, and in this form, is less toxic than inorganic or organic bound mercury. It has a high vapor pressure. If heated, mercury evaporates and becomes highly toxic. Metallic mercury is lipophilic and is stored in fatty tissues.4 Inorganic ions of mercury vary in water solubility. In general, divalent mercuric salts are soluble in water. The high toxicity of mercuric ions can be explained by the high affinity to sulfhydryl groups of amino acids, which are building blocks for enzymes. In organic mercury compounds, mercury is covalently bound to carbon. Organic mercury is the most dangerous form of mercury to human health. Methylmercury, the most predominant form of organic mercury, is the form that poses a risk through fish consumption. Methylmercury is better absorbed and shows a higher mobility in the human body than inorganic mercury. Another example of an organic mercury compound is ethyl mercury or thiomersal (referred to as thimerosal in the USA), which is used as a preservative in some vaccines.

Mercury is of global concern. The United Nations Environment Programme (UNEP) assessed the global mercury burden.5 Mercury is now a priority matter in the European Union.6, 7 Progress has been made toward an anthropogenic mercury-free environment but it still remains a significant threat in developing countries.5 In 2006, the International Conference on Chemicals Management adopted the “Dubai Declaration on International Chemicals Management,” the “Overarching Policy Strategy,” and endorsed the “Global Plan of Action,” in which priority attention is given to mercury.8, 9 These 3 documents constitute the Strategic Approach to International Chemicals Management. The intergovernmental forum on chemical safety expressed concern about mercury and other toxic metals in “The Budapest Statement on Mercury, Lead, and Cadmium.”10 The scientific community expressed their concern about mercury and other heavy metals in “The Declaration of Brescia on Prevention of the Neurotoxicity of Metals.”11 UNEP has a special ad-hoc open-ended work group on mercury (http://www.chem.unep.ch/mercury/OEWG2/Meeting.htm).

Section snippets

Mercury in the Environment

Mercury pollution of the environment has natural, anthropogenic, and historic sources.1, 5 The proportion of anthropogenic mercury nearly doubled within the last 100 years and with about 70% distinctly outweighed naturally released mercury.12 The mercury problem is mainly a man-made problem and therefore can be minimized by implementing efficient measures. Mercury is not only anthropogenic, it also occurs naturally. Natural mercury releases can be caused by volcanic activity, weathering of

Diagnosis of Mercury Intoxication

A medical history, including an environmental history, a complete physical examination, plus results of mercury measurement in human tissue can exclude or substantiate the diagnosis of mercury intoxication. It is important to handle the collection and analysis of urine and blood mercury tests carefully.67

Analytical Methods and Quality Assurance

For the assessment of mercury in specimens, it is essential to ensure the quality of the analysis.211 Reference material should be as close in chemical composition to that of the sample and should also contain the analyte at about the same concentration as is present in the sample. More information on reference material can be found under http://www.VIRM.net or http://www.rt-corp.com/products. Certified reference material is available.

Speciation might be necessary for proper risk assessment.

Surveys, Including Human Exposure Measurements

There are several surveys that included measurements of exposure to mercury. These surveys are important to identify trends in exposure, exposure patterns, vulnerable subgroups, and exposure hot spots.211 Some examples will be given. Other surveys are available at the regional level.

Environmental Monitoring

Monitoring the environment for mercury indicates the extent of external mercury exposure for children. Media used for environmental monitoring include the following4, 5, 226:

  • Air: Mercury can be analyzed in air, either with personal mercury vapor samplers, which are analyzed latterly using atomic absorption spectrometry, or with passive diffuse samplers. Mobile analyzers, such as, eg, the Lumex, can measure elemental mercury in air continuously.

  • Food: Mercury can be analyzed in food and other

Environmental Guidelines

Guidelines for water, air, and soil have been set nationally and internationally. International guidelines for air, water, soil and food are as follows:

Air: The World Health Organization guideline value for inorganic mercury vapor is 1 μg/m3 as an annual average.227 A tolerable concentration is 0.2 μg/m3 for long-term inhalation exposure to elemental mercury vapor, and a tolerable intake of total mercury is 2 μg/kg body weight per day.70

Fish: Food and Agriculture Organization/World Health

Preventing Mercury-Related Human Health Effects

Because mercury is hazardous to children's health, attention needs to be drawn to prevention.

Short Term

Develop mercury clean up and waste handling and storage procedures. Until countries in transition and developing countries have access to mercury-free alternatives, it is imperative that safe handling procedures be instituted that minimize and eliminate patient, occupational, and community exposures. Proper procedures should include spill clean-up response, educational programs, protective gear, appropriate waste storage containment, staff training, and engineered storage facilities. Countries

Acknowledgments

The authors are grateful to Drs Alessandro Alimonti, Nida Bisbelli, Marcello Conti, Paul Dargan, Jules de Kom, Gustav Drasch, Jenny Pronczuk, and Ellen Silbergeld for their contributions to this work.

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