Must dos for Mercury exposure

Medical monitoring is the periodic evaluation of exposed workers to ensure that they are experiencing no adverse effects of potentially hazardous workplace exposures. It serves as a back-up for a program of routine air and biologic monitoring, which is the primary means for ensuring that exposure levels are below those associated with adverse health effects. A medical monitoring program should be designed to detect adverse effects of exposure as early as possible, at a stage where they are still reversible, so that exposures can be controlled and serious permanent adverse effects prevented.

Baseline and periodic examinations
An initial medical examination should be performed on all employees exposed to potentially hazardous levels of mercury. The purpose of this examination is to provide a baseline for future health monitoring.

The examination should include a complete medical history and symptom questionnaire, with emphasis on the nervous system (target organ for chronic exposure to Mercury), the kidneys (target organ for acute and chronic exposure), the oral cavity (target organ for chronic exposure), the lungs (target organ for acute exposure), the eyes (affected by chronic exposure), and the skin (since mercury is a known skin sensitizer). Signs and symptoms of the earliest signs of mercury intoxication should be elicited; these include personality changes, weight loss, irritability, fatigue, nervousness, loss of memory, indecision, and intellectual deterioration. Complaints of tremors and loss of coordination should also be sought. Physical examination should focus on the target organs described above. A baseline handwriting sample should be obtained. Laboratory evaluation should include, at minimum, a complete urine analysis (see below).

This examination should be repeated annually. Results should be compared with the findings on the baseline examination for changes suggestive of mercury toxicity. Handwriting samples should be compared to the baseline sample for evidence of tremor. Interim evaluations should be conducted if symptoms suggestive of mercury intoxication are occurring.

Confidentiality of the Medical Information
The Questionnaire and physical examination results for periodic examination should be compared to the baseline examination to detect any change which might be attributed to mercury intoxication. The results should be conveyed in detail to the worker. The employer should be informed by the examining physician if mercury intoxication is suspected on the basis of symptoms or results of the physical examination or laboratory tests. If intoxication is suspected, the worker should be removed from exposure and expert medical consultation should be sought. Otherwise, the results of the physical exam should be kept confidential, and no management personnel other than health professionals should have access to the medical records.

Importance of evaluating group results
The results of the questionnaire and physical examination should also be evaluated on a group basis. This is important because early mercury poisoning might cause only very mild, clinically insignificant increases in symptomatology in each individual which, when seen in the aggregate, might provide an important clue that toxic exposure to mercury is taking place.

Who should perform the medical examinations?
All medical monitoring of exposed employees should be conducted by a physician knowledgeable in occupational medicine. In particular, interpretation of the group data should be undertaken only by a trained occupational health physician or other physician with expertise in performing such analyses.

Using more sensitive medical tests
Several studies have shown that some special tests may be useful in detecting early signs of mercury toxicity.

Neurobehavioral tests, designed to detect early changes in concentration, response time, memory, and hand-eye coordination, can be useful on both an individual and a group basis in detecting early nervous system effects of mercury exposure.

Early kidney damage may be detected by looking for the presence of low molecular weight proteins in the urine. The presence of these proteins in the urine indicates that kidney damage has occurred long before a routine urinalysis indicates an abnormality. Beta2 microglobulin and N-acetyl-B-D glucosaminidase (NAG) are two of the proteins which can be measured in the urine. The tests are useful on both an individual and group basis.

These special tests should be arranged for and interpreted by a trained occupational physician or other physician with special expertise in these areas.

BIOLOGIC MONITORING
Biologic monitoring is the measurement of chemical agents in the blood, urine, or other body tissue of exposed individuals to determine how much of the chemical has been absorbed into the body. It serves as a back-up to environmental exposure measurements, since air measurements cannot assess skin exposure or the effects of protective equipment and work practices. Since it measures the amount of an agent actually absorbed into the body, it is usually a better estimate of risk for adverse health effect than air monitoring. There is no ideal biologic monitor for evaluating the risks of mercury intoxication from metallic or inorganic mercury. Mercury can be measured in both blood and urine. Individual levels may vary greatly from day to day and even within a given day. While proper interpretation of the results can be difficult, the measurements can nevertheless provide information on potential overexposure. Measurements should be carried out regularly (several times per year) in chronically exposed workers, and individual as well as group results should be evaluated. Baseline levels should be obtained before exposure begins for comparison purposes.

Mercury in Urine
Measurement of mercury in urine is the recommended biological monitor for workers exposed to metallic and inorganic mercury. Ideally, the collection should be over 24-hours, but this is seldom feasible. Spot urine samples may also be taken, but care must be taken to always collect them at the same time of day near the end of the work week after several months of steady exposure. Overnight samples may also be collected; this collection extends from the time the employee goes to bed through the first urination of the morning.

Samples must be collected in containers provided by the laboratory, since a preservative must be added. At least 25 cc of urine must be collected. Great care must be taken to prevent contamination of the sample containers or the urine with mercury from the skin or workplace air.

When results are interpreted, the urine values should be corrected for grams of creatinine in the sample, and should be expressed as ug Hg/gram creatinine. In persons not occupationally exposed to mercury, urine levels rarely exceed 5 ug/g creatinine.

While many laboratories indicate that only levels above 150 ug/L should be considered toxic, there is strong evidence that early signs of mercury intoxication can be seen in workers excreting more than 50 ug Hg/L of urine (standardized for a urinary creatinine of 1 gram/L). This value of 50 ug/g creatinine is proposed by many experts as a biological threshold limit value for chronic exposure to mercury vapor, and in 1980 this was endorsed by a World Health Organization study group.

Exposed individuals with levels above 50 ug/g creatinine should be placed in a non-exposed job until the reason for their overexposure has been identified and corrected and their urine levels have fallen below the biologic threshold limit value.

Mercury in blood
The concentration of mercury in blood reflects exposure to organic mercury as well as metallic and inorganic mercury; thus it can be influenced by the consumption of fish containing methylmercury.

Samples should always be taken at the same time of day near the end of the work week after several months of steady exposure. The blood should be collected in mercury-free heparinized tubes after careful skin cleansing.

In unexposed individuals, the amount of mercury in blood is usually less than 2 ug/100 ml. According to some experts, an average airborne concentration of 50 ug/m3 corresponds to a mercury concentration in blood of about 3-3.5 mg/100 ml. Early effects of mercury toxicity have been found when the blood concentration exceeds 3 ug/100 ml. Any worker exceeding this level should be placed in a non-exposed job until dietary and workplace exposures have been evaluated and blood levels have returned to baseline.

Removing Employees from Exposure
An individual who must be removed from mercury exposure because of elevated blood or urine mercury levels or physical examination results suggesting early mercury intoxication should be given alternative work with no exposure. His or her wages, benefits and seniority should be maintained. No employee should be terminated or otherwise punished because of overexposure to mercury.

In the event that no job without mercury exposure is available, the employee may continue to work using a supplied air respirator, provided that biological monitoring results and/or symptoms display a satisfactory decline over time.

References:
1. New Jersey State Department of Health. Division of Occupational and Environmental Health
2. Janet Raloff . Landfills Make Mercury More Toxic. Sceinece News Online. Jul 17th 2001 Vol 160 No 1
3. State Environmental Resource Center. : info@serconline.org
4. Melissa Lee Phillips, Abraham Lincoln and His Little Blue Pills.Did Lincoln Suffer from Mercury Poisoning? Neuroscience for Kids Consultant July 10, 2002