Making sence of lead blood limits.

The health effects due to exposure to lead vary greatly between individuals and depend on a variety of factors such as a person’s age, the amount of lead a person is exposed to and for how long, and if they have other health conditions.

According to the recent HSE statement there is growing scientific evidence that employees' health is at risk, even where exposure to lead is below the levels in CLAW. The current suspension levels for a worker other than a young person or a woman is 60 µg/dl (blood) or  110 µg Pb/g creatinine (urine).

The HSE states that above levels of 40ug/dl, the following health effects have been observed:

• changes in the blood which might lead to anaemia
• effects on the nervous system
• effects on the kidney  
• altered functioning of the testicles which could lead to infertility

At exposures around 30ug/dl, elevated blood pressure in middle-aged males has been reported.  Blood lead levels at which people exhibit symptoms vary greatly between individuals. It is possible for people with blood lead levels of 40 micrograms per decilitre or more not to exhibit noticeable health effects.

The mechanism of lead absorption.

Lead is not readily absorbed through the skin. People absorb lead into the body by breathing lead-contaminated air or swallowing lead-contaminated particles. The proportion of lead that is absorbed depends on several factors including the solubility of the lead contaminant, the size of the lead particles and the person’s age, sex, and diet.

Once in the lungs or gut, lead is absorbed into the bloodstream and is distributed to the liver, kidneys, lungs, brain, spleen, muscles, and heart, and can be stored in bones and teeth. Lead that has been stored in bones and teeth can be released many years after exposure.

When should lead blood levels be measured?

Measurement of blood lead should be considered when symptoms or health effects associated with lead are present and/or a source of lead exposure is suspected. In the context of the compliance with the CALW regulations the lead blood test should be carried out on workers when there is a risk is significant. This is further defined as where the employees are

1. liable to be exposed to a concentration of lead in the atmosphere exceeding half the occupational exposure limit for lead (WEL:0.15mg/m³);
2. where there is a substantial risk of any employee ingesting lead; e.g in situations where employee’s hands or face are so liable to be contaminated by lead that there is a high risk that the lead could then be ingested.
3. where there is a risk of contact between the skin and lead alkyls or other substances containing lead which can be absorbed through the skin;  

A blood lead test generally detects lead that the person has breathed or swallowed within a few weeks or months of testing. If a person has been exposed to a steady, small amount of lead (rather than a larger amount from an unusual source), blood lead is a reliable indicator of their level of exposure, especially if several measurements are available. However, if a person has been exposed to a large amount of lead, a blood lead test will not indicate the total amount of lead in a person’s body. This is because the lead circulating in the body is excreted by the kidneys or liver (in urine and faeces) and the remainder is stored in bone. This stored lead may be released back into the blood at a later time.

How serious is lead in blood?

The effects of blood lead levels less than 10 micrograms per decilitre are unlikely to result in noticeable health effects in an individual. The review of scientific and government publication around the word and in the UK shows that blood lead levels greater than 10 micrograms per decilitre have adverse effects on the body’s digestive, cardiovascular, renal, reproductive and neurological functions.

If blood lead levels are reported to be between 10 and 20 micrograms per decilitre this and indication that a person has been, or continues to be, exposed to sources of lead that may result in adverse health effects. The effect may be very mild or not manifested at all in male adult workers. However, it is still recommended to undertake and follow up blood test after the source of exposure has been remediated to confirm that the lead blood levels have been reduces to negligible level.

If lead blood levels are reported to be between 20–44 micrograms per decilitre it is indicative that a person has been or continues to be exposed to source of lead that may result in noticeable health effects. Workers may suffer with acute symptoms of lead exposure, such as gastrointestinal disturbances (e.g. nausea, vomiting, constipation and abdominal pain) and neurobehavioural effects (e.g. forgetfulness, irritability, headache and fatigue) in adults.

If blood levels are reported to be in the range of 45–69 micrograms per decilitre this is that a person has been exposed to a harmful level of lead that may result in acute symptoms of lead exposure. Acute symptoms of lead exposure may include gastrointestinal disturbances (eg. nausea, vomiting, constipation and abdominal pain), neurobehavioral effects (eg. forgetfulness, irritability, headache and fatigue) pallor and muscle weakness. Environmental intervention including exposure evaluation, environmental investigation, risk assessment and management of the exposure source should be undertaken.

If lead blood levels are reported above 70 micrograms per decilitre this indicates a medical emergency.