Review Lead and mercury exposures: interpretation and action Elizabeth Brodkin, Ray Copes, Andre Mattman, James Kennedy, Rakel Kling, Annalee Yassi received treatment from an alternative health care provider. Abstract These cases have been chosen to illustrate some of the issues that commonly arise around concerns of exposure to heavy Lead and mercury are naturally occurring elements in the metals, in particular lead and mercury. We also provide a earth’s crust and are common environmental contaminants. guide to interpreting laboratory investigations to assist clini- Because people concerned about possible exposures to cians with investigating concerns and advising their patients. these elements often seek advice from their physicians, clini- cians need to be aware of the signs and symptoms of lead Cases and mercury poisoning, how to investigate a possible expo- sure and when intervention is necessary. We describe 3 Case 1 cases of patients who presented to an occupational medi- cine specialist with concerns of heavy metal toxicity. We use A 54-year-old East Indian man consulted his family physician these cases to illustrate some of the issues surrounding the because of fatigue, abdominal pain, nausea, headaches and investigation of possible lead and mercury exposures. We re- weight loss. Investigations ordered by the family physician in- view the common sources of exposure, the signs and symp- toms of lead and mercury poisoning and the appropriate use cluded measurement of the hemoglobin concentration, which of chelation therapy. There is a need for a clear and consis- was 73 g/L. The pathologist who reviewed the laboratory test re- tent guide to help clinicians interpret laboratory investiga- sults commented on the low mean cell volume and coarse ba- tions. We offer such a guide, with information about popula- sophilic stippling of the red blood cells. The blood lead level tion norms, lead and mercury levels that suggest exposure was therefore measured and found to be markedly elevated, at beyond that seen in the general population and levels that 4.15 (reference range < 1.93) μmol/L. It was eventually deter- warrant referral for advice about clinical management. mined that the patient had been taking traditional medicines imported from India for over 2 years. Analysis revealed that they CMAJ 2007;176(1):59-63 contained 13%–14% (130 000 μg/g) lead and 1% (10 000 μg/g) mercury by weight. The patient was referred to a clinical toxicol- xposure to environmental contaminants, including ogist and underwent chelation therapy, with substantial im- heavy metals, continues to be a widespread problem provement of his symptoms and anemia. At follow-up several E in Canada, and patients concerned about possible ex- months after his last chelation treatment, his blood lead level posures often seek advice from their physicians. Heavy met- was 1.34 μmol/L and hemoglobin concentration 129 g/L. als are a well-established cause of severe illness, and these concerns need to be addressed. However, although clini- Case 2 cally significant exposures to heavy metals still occur in Canada, a substantial proportion of patients who present A 35-year-old dentist presented with a 1-year history of a fine with concerns of heavy metal toxicity do not have true poi- resting tremor in his hands. This is a serious occupational dis- soning. Physicians need to be aware of not only the signs and ability for him, because it interferes with his ability to perform symptoms of heavy metal poisoning but also what investiga- the fine motor tasks required in dental practice. He was assessed tions are appropriate, how to interpret the results, when in- by a neurologist, who diagnosed benign tremor. The patient be- tervention is necessary and when it is unwarranted. Alterna- came concerned about possible mercury toxicity because of tive health care providers are also investigating and treating some occupational exposure to mercury and asked his family heavy metal exposures; therefore, it is helpful to be familiar physician to arrange for testing. Results from tests conducted at with the treatments they are offering and some of the pit- a laboratory in Quebec City revealed that his blood mercury level falls their patients may fall into. was 18 (reference range < 15) nmol/L, and his mercury level in a In this review, we describe 3 cases of patients referred to an 24-hour urine collection was reported as “normal.” The patient occupational medicine specialist with concerns of heavy metal began reducing his exposure to mercury amalgam and requested toxicity. One was referred with symptoms of severe poisoning a consultation with an occupational medicine specialist to dis- from an unknown source, the others with significant anxiety cuss chelation therapy. Repeat testing at a laboratory in Vancou- about possible occupational exposures and conflicting labora- ver revealed a blood mercury level of 19 (reference range < 29) DOI:10.1503/cmaj.060790 tory investigations. One patient had already consulted and had nmol/L and a mercury level in a 24-hour urine collection of 29 CMAJ • January 2, 2007 • 176(1) | 59 © 2007 Canadian Medical Association or its licensors Review (reference range < 50) nmol/d. The patient was not reassured by Inorganic and organic forms of lead are absorbed through these results, since he found the different reference ranges used the lungs and gastrointestinal tract; organic lead compounds by the 2 laboratories confusing. may also be absorbed through the skin. In occupational set- tings, exposure through inhalation is more common, where- Case 3 as in the general population it is largely through ingestion.9 Following absorption, lead is taken up in the blood and de- A 44-year-old woman worked for 10 months in a car dealership posited in soft tissues (brain, liver, kidney, bone marrow) and and service centre. In the course of her work, she was exposed bone. Excretion is primarily via the kidneys, and the half-life to vehicle emissions and other substances present in the service of lead in the blood is about 30 days. Up to 94% of the body area. There was no established exposure to heavy metals. The burden of lead is in bone, where it has a half-life of years to woman developed a variety of symptoms, including pain and decades.3,9 Pregnancy, lactation, menopause, osteoporosis tingling in one hand, abdominal pain and bloating, diarrhea and other events that lead to increased bone resorption will and constipation, increased bruising, varicose veins and fa- lead to an increase in blood lead levels in people who have tigue. After 10 months she left the car dealership. Her symp- substantial amounts of lead stored in bone, and it can be an toms improved, but she remained concerned and consulted an unexpected source of lead poisoning.9 alternative health care provider. He arranged testing for blood Signs and symptoms of lead poisoning in adults may in- lead and blood mercury levels and a “24-hour urine toxic met- clude abdominal pain, anorexia, nausea and constipation, als test,” which entailed challenging the patient with a chelat- headache, joint and muscle pain, difficulties with concentra- ing agent and subsequently measuring the levels of various tion and memory, sleep disturbances, anemia with basophilic heavy metals in her urine. Her blood lead level was 0.1 (refer- stippling, peripheral neuropathy and nephropathy.3,9 ence range < 1.93) μmol/L and her blood mercury level 10 (ref- The blood lead level is the most widely used and most reli- erence range < 29) nmol/L. However, the results of the toxic able measure of lead exposure. It primarily measures expo- metals test were presented in such a way as to suggest lead and sures that have taken place in the previous few weeks10 but is mercury toxicity. The alternative health care provider diagnosed a poor indicator of lead accumulated in bone. Bone lead levels heavy metal poisoning from her working at the car dealership are theoretically the best indicator of total body burden; how- and started the patient on chelation therapy. The patient’s fam- ever, measurement is difficult. X-ray fluorescence can be used ily physician questioned this course of action and arranged for to monitor lead in the skeleton, but the technique is not consultation with an occupational medicine specialist. widely available and is generally used only for research.11 Contamination of blood and urine specimens during collec- Lead tion and storage is a potential problem when screening for heavy metals, and adherence to strict guidelines from a rep- Lead is used in many industries, including lead smelting and utable laboratory is important. The use of metal-free collec- processing, the manufacturing of batteries, pigments, solder, tion devices and storage tubes is essential. plastics, cable sheathing, ammunition and ceramics, and bat- Interpretating blood lead levels requires an understanding tery recycling.1 In the United States, most cases of lead poison- of reference ranges and how they are derived. Although lead ing in adults result from occupational exposure, although lead is toxic and serves no biological purpose, it is a naturally oc- exposure in the general population is primarily through diet.2 curring element, and some degree of exposure is universal. Whether the same is true in Canada is uncertain, since popula- Reference ranges may vary from laboratory to laboratory; in tion-based surveillance of exposure to lead or other environ- some cases they are based on levels commonly or normally mental contaminants is not performed in