«The report was independently reviewed by an environmental toxicology specialist, Professor Michael Moore. Professor Michael R. Moore Director of the ...»
This report was prepared by Environmental Health Services of the Tropical Population Health
Network, Northern Area Health Service, Queensland Health.
The report was independently reviewed by an environmental toxicology specialist, Professor Michael
Professor Michael R. Moore
Director of the National Research Centre for Environmental Toxicology (EnTox).
University of Glasgow; B.Sc., Honours, Biochemistry, 1967; Ph.D., Medicine, 1971D.Sc., Biochemistry in Medicine 1987 Michael is a registered toxicologist (Eurotox & Institute of Biology, UK) and Registrar of the Australasian College of Toxicology and Risk Assessment (ACTRA). He is Professor in Medicine at the University of Queensland and Adjunct Professor in: Griffith University; University of the Sunshine Coast; Queensland University of Technology. He is also a co-director of the Australian Centres for Human Health Risk Assessment.
As an international expert in toxicology of water pollutants relevant to public health, his areas of expertise include the toxicology of metals, air toxics, risk assessment, cyanobacterial toxins and disorders of porphyrin metabolism.
He is a prolific producer of research outputs with more than 500 referred publications and numerous books and book chapters to date.
Copies of this report may be obtained by contacting the Tropical Population Health Unit – Mount Isa and Gulf on (07) 4744 4846.
Date: May 2008 Executive Summary There is a long history of lead mining and associated activities in Mount Isa. This combined with naturally occurring lead in the environment and its persistence mean that there are elevated levels of lead in parts of the environment of Mount Isa. The presence of lead in the environment and its potential to elevate blood lead levels in those living and working there has been acknowledged for many years. The ongoing collaboration between the mining company, the Mount Isa City Council and various state government agencies, including Queensland Health has therefore focused on ways to manage potential lead exposures and provide advice and support for the families of children found to have elevated blood lead levels.
At the population level, past epidemiological studies have reported adverse health effects in young children at blood lead levels of 10 μg/dL and above. Exposure to lead in early childhood is associated with impaired cognitive development. Features of high blood lead levels may include reduced attention span, reduced spatial skills, poorer performance at school, haematological changes, and behavioural problems. Though there is no current specific health guideline in Australia for blood lead levels Queensland Health has adopted the public health goal of achieving blood lead levels below 10 μg/dL concordant with WHO standards in order to best manage community lead exposure in Queensland. At blood lead levels less than about 20 μg/dL however, clinical symptoms or signs of acute toxicity would not be expected.
In 2006, Queensland Health commenced a study in Mount Isa of children between one and four years old in order to determine blood lead levels in this age group. Children were recruited by invitation. The 400 recruited for the study were found to be representative of the general population of one to four year olds in Mount Isa in terms of age, sex and Indigenous status.
Children were encouraged to be tested over a period of 14 months through an extensive media campaign titled ‘Get Bled for Lead’. The ‘Get Bled for Lead’ campaign served two purposes – it provided awareness and information on how to participate in the study and also provided general information to the community on how to minimise their potential lead exposure.
Results of the study indicate that the average blood lead level (geometric mean) for the group of children sampled was 5.0 μg/dL, with a minimum value of 1.3 μg/dL and maximum value of 31.5 μg/dL. Forty-five children (11.3% of those in the study group) had blood lead levels greater than or equal to 10 μg/dL. Of these, two children had blood lead levels greater than 20 μg/dL.
Statistical analyses revealed significant associations between blood lead levels greater than or equal to 10 μg/dL and Indigenous status and age. Indigenous children were approximately four times more likely (OR 4.3) to have a blood lead level of greater than or equal to 10 μg/dL than non Indigenous children. For all participants the likelihood of having a blood lead level of ≥10 μg/dL was found to be reduced by 4% for every one month increase in age. Analysis also demonstrated no statistically significant associations between blood lead levels and the variables of sex or length of time in Mount Isa.
Household audits carried out for those children with elevated blood lead levels (equal to or greater than 10 μg/dL) indicated that factors such as chewing, sucking or eating non food items, residing in a property with bare soil and pet ownership were common in this group. These factors have been consistently reported to be associated with elevated blood lead levels in children in studies at other locations.
On the basis of results of the study, Queensland Health has focused on a range of individual follow up activities as well as continuing population focused strategies for improving awareness and encouraging behavioural modification for the greater Mount Isa community. For those households where children had elevated blood lead levels, individual follow up activities will continue to focus
auditing of environments and collection of soil/paint/dust samples at other places where the child spends significant time, advice with modifying the home environment, and identifying child hand-mouth behaviours and practices that may lead to exposure, dietary investigation and advice, additional blood testing to determine if exposure prevention strategies are reducing blood levels, and referral to a paediatric specialist where blood lead results are above 20 μg/dL.
Queensland Health continues to encourage community uptake of the free blood lead testing service at Queensland Medical Laboratory Pathology Services and will closely monitor results of any testing.
In addition Queensland Health will continue to work with key partners through the Living with Lead Alliance to develop long term strategies for lead management in Mount Isa.
2.0 Study rationale
3.0 Study aims
4.0 Study methods
4.1 Blood lead sampling
4.2 Household audit
4.3 Data Analysis
5.0 Study results
5.1 Participant characteristics
5.2 Blood lead levels for participating Mount Isa children
5.3 Household factors
7.0 Queensland Health response
Mount Isa was established because of the vast mineral deposits in its immediate vicinity.
In 1923, John Campbell Miles discovered a rich seam of silver-lead ore on the western edge of the Cloncurry mineral field at Mount Isa. Copper and zinc are also mined in the area. Copper, lead and silver are smelted on site, with products transported 900km to Townsville.
Xstrata Plc currently operates the Mount Isa Mines facility, which is located to the immediate west of the city. The Mount Isa Mines complex includes crushing plants, mills, concentrators and two smelters. The mining sector is the largest employer in the Mount Isa region, employing around 27% of the region’s employed population (ABS 2006c).
what is lead?
Lead is a dense, low melting point, bluish-grey metal that occurs naturally in the Earth’s crust.
However, it is rarely found naturally as a metal. It is usually found combined with two or more other elements to form lead ores which are mined and smelted. Lead is a metallic element and cannot degrade.
Even though lead occurs naturally in the environment, most of the high levels found throughout the environment come from human activities. Lead can enter the environment through releases from mining lead and other metals, and from factories that make or use lead, lead alloys, or lead compounds. Lead is released into the air during burning coal, oil, or waste. Before the use of leaded petrol was banned, much of the lead released into the Australian environment came from vehicle exhaust. Another common source of lead was lead-based paint. Though the amount of lead in household paint was significantly restricted in the early 1970s, it still exists in the paint of older homes throughout Australia.
The greatest increase in environmental levels of lead, in most locations, occurred between the years 1950 and 2000. This was mainly due to increasing worldwide use of leaded petrol. Since the introduction of unleaded petrol in Australia in 1996, the reduction in lead content of leaded petrol from 0.84g/L in 1990 to 0.2g/L in 1996, and then the complete ban of leaded petrol in 2001, there has been a steady decline of levels of motor vehicle-related lead in the air in monitored sites in Queensland. This decline has been so significant that the Environmental Protection Agency’s airborne lead monitoring program (relating to motor vehicle lead emissions) ceased at the end of 2002 (EPA, 2003).
how are people exposed to lead?
The general population may be exposed to lead in ambient air, foods, drinking water, soil, and dust. Segments of the general population at the highest risk of health effects from lead exposure are preschool-age children and pregnant women and their fetuses. Other segments of the general population at high risk include individuals living near sites where lead is or was produced or disposed of, and people who work with lead.
Exposure to lead occurs mainly through ingestion and inhalation of dust and air contaminated by lead. Children commonly play in dirt and dust and their hand-to-mouth behaviour means that ingestion of lead is an important pathway (Simon et al., 2007, Ko et al., 2007).
Extreme cases of this hand-to-mouth behaviour are referred to as pica. Pica is an eating disorder typically defined as the persistent eating of non-nutritive substances for a period of at least one month at an age at which this behaviour is developmentally inappropriate (e.g. 18-24 months).
Pica is most common in young children in their second and third years of life (Ellis and Schnoes, 2006).
role of diet One of the keys to minimising the effects of lead in children is to minimise the amount of lead that actually gets absorbed into their system. A child’s body needs certain minerals such as calcium and iron, and when these minerals are deficient in the body, lead absorption is increased.
Good nutrition, which includes an adequate intake of calcium and iron, lowers the proportion of swallowed lead that passes to the bloodstream. Various studies have shown that gastrointestinal absorption is greater when the stomach is empty. Pulmonary absorption is generally greater than gastrointestinal absorption.
blood lead levels in australia Blood lead levels are commonly used as a marker of exposure to lead in humans and are generally reported in micrograms (μg) per decilitre (dL) of blood. The blood lead level of a newborn baby typically reflects that of the mother and as infants become more active and increase their environmental exposure, their blood lead levels increase. Studies of lead exposed children typically show that blood lead levels increase in late infancy and peak between 18 to 36 months of age (Binns et al, 2007). This relates to increased activity and increased potential for environmental exposure.
The last national survey of blood lead levels in Australia was conducted in 1995 by the Australian Institute of Health and Welfare (Donovan J, AIHW, 1996), where 1575 children aged 12-60 months from all states and territories were sampled. Results indicated that of the children sampled for the study, 92.7% had blood lead levels 10 μg/dL, 7.3% had blood lead levels ≥ 10 μg/dL, 1.7% had blood lead levels ≥ 15 μg/dL and 0.25% had blood lead levels ≥ 25 μg/dL. The mean (arithmetic) blood lead level was 5.72 μg/dL and the mean (geometric) blood lead level was 5.05 μg/dL. The maximum blood lead level reported was 32.7 μg/dL. For Queensland, where 270 children were sampled, the arithmetic mean was 5.59 μg/dL and 95.2% of the sample had blood lead levels 10 μg/dL.
health effects of lead exposure
Children under the age of five are at greatest risk of health effects of lead exposure. This is because:
the brain in young children is still maturing and appears to be more vulnerable to lead exploratory hand-to-mouth activity of children places them at higher risk of ingesting lead from a contaminated environment children absorb a much higher proportion of ingested lead than adults (40 - 50% compared to 3
- 10% for adults).
Population-based epidemiological studies have found exposure to lead in early childhood to be associated with impaired cognitive development (ATSDR, 2007). At blood lead levels less than 20 μg/dL, clinical symptoms or signs of acute toxicity would be unexpected. Symptoms of higher blood lead levels may include reduced attention span, reduced spatial skills, poorer performance at school and behavioural problems. Lead can pass from mother to the unborn baby and therefore maternal exposure to lead in pregnancy can affect the unborn baby.
Symptoms in adults depend on the level of exposure. High levels can cause joint and muscle pain, muscle cramps, anaemia, nausea, constipation, colicky abdominal pain, sleep problems, reduced concentration and headaches. At very high levels (greater than 80 μg/dL) lead may cause encephalopathy (i.e. a disease of the brain) and convulsions. Lengthy high level exposure to lead can also be associated with chronic renal damage.
is there a ‘safe’ level?