Very little is known about the spectrum of causes of Attention Deficit Hyperactivity Disorder and Attention Deficit Disorder. One possible cause that has come to light in recent years, but has received little attention in Australia, is the role of environmental toxins, especially lead.

Health effects

Lead is a potent nerve poison that adversely affects many systems in the body. The organ systems that are particularly sensitive to lead are the central nervous system (specifically the brain), the kidney and blood-forming tissues. Recent studies have shown adverse neuro-psychological effects (e.g. reductions in IQ) at blood lead levels previously thought to be safe (10-15 µg/dL [micrograms per decilitre]).

In his landmark study, Needleman (1979) showed that behavioural and performance problems in primary school children which included hyperactivity, distractibility, impulsivity, disorganisation, non-persistence, inability to follow simple instructions and overall poor functioning, were more prevalent with increasing dentine (teeth) lead levels. Furthermore, in a recent long term follow-up study (Needleman et al., 1990), for children who had been exposed to moderate lead levels (greater than 20 ppm [parts per million] in dentine lead) in preschool years, the odds of those children dropping out of high school were seven times higher, and the odds of a significant reading disability were six times higher than for children exposed to lower lead levels. Children exposed to higher lead levels were also shown to have problems with attention and fine motor skills, lower standing in class, increased absenteeism, and lower vocabulary and grammatical-reading scores, even after the investigators controlled for other variables. Sciarillo (1992) found that 2-3 year old children with blood lead levels greater than 15 µg/dL were twice as likely to have sleep problems, were five times more aggressive, four times more destructive and two and a half times more likely to have somatic problems than children with blood lead levels below 15 µg/dL.

It must be stressed that lead is possibly only one of many causes of attention deficits, learning difficulties and behavioural problems in children. However, childhood lead exposure is one problem we know is present in many communities and one we know how to control.

High Risk Groups

In general, infants and children are affected much more by lead exposure than adults since children:

• take in larger quantities of soil and dust than adults, through normal hand-to-mouth and play activities;
• absorb a higher proportion of the lead they take in than do adults, approximately 50% compared with adults who absorb only 8-10%. Also:
• lead is more harmful to the developing brain, nervous system and other metabolic activities of children.

Pregnant women (as surrogates for foetuses) are also a sensitive population and lead workers have long been recognised to be at risk because of excessive exposure.

(The ADD Child in the Classroom, illustration by Anne Roberts)

Sources of lead include:

• Lead-based paint - the most common source of high dose lead exposure, responsible for the majority of cases of clinical poisoning in children;
• Lead in petrol - provides a small but significant dose for the whole population;
• Stationary sources - e.g. smelters and mines may provide a high dose source for the surrounding community;
• Contaminated dust and soil - as a legacy of past production of lead, as well as past uses in paint, petrol and other sources;
• Occupational and hobby exposure - e.g. battery breaking, lead-lighting;
• Drinking water - minor source for the whole population;
• Lead in food - a small percentage of food cans in Australia are lead-soldered.

Ways to reduce exposure

Keep pregnant women and children away from homes (pre 1970's buildings may contain lead-based paints) which are undergoing renovations. Ensure soft furnishings and carpets are removed from the work area or covered by plastic. Do not use equipment that may liberate hazardous dusts and fumes (e.g. sanders, heat guns). Thorough clean-up must be undertaken at the end of the days work and at the completion of the job.The work areas should be vacuumed with a HEPA [high-efficiency particulate air] filter equipped vacuum cleaner, and all surfaces cleaned by wet mopping/wiping.

Dust in ceilings will often be lead contaminated. If cornices are in good condition then the risk of "dust leakage" is probably low and in some cases a worse situation may be created by disturbing the dust. If you are considering building an attic or adding a second storey, dust should be removed.

Many pre-1960 premises may have contaminated soil especially around the perimeter of the dwelling. These areas must not be allowed to be accessed by children and good ground cover (e.g. grass) should be maintained at all times.

Other important measures that help reduce lead hazards include:

• Ensuring diet is adequate in calcium, iron, zinc and not excessive in fat;
• Washing children's hands and face regularly, particularly before eating;
• Wet mopping all floors (avoid dry sweeping) and wet wiping window sills and wells with high phosphate (5-8%) detergents (avoid feather dusting);
• Washing toys and dummies frequently;
• Do not store food in open cans, particularly if they are imported;
• Use only fully flushed cold water for drinking, cooking and preparing infant formula;
• Ensure take-home exposures are not occurring from parental occupations/hobbies;
• Washing vegetables before consumption.

Is your child at risk of lead poisoning?

Excessive absorption of lead is one of the most prevalent and preventable childhood health problems in most industrialised countries today. There is considerable evidence that even very low blood levels of lead may have a deleterious effect on the foetuses of pregnant women and on young children .

In response to this evidence the National Health and Medical Research Council in June 1993 set a goal of below 10 µg/dL [equivalent to 0.48 micromoles per litre (1mol/L)] lead in blood, for all Australians. The Council stresses the urgency of achieving this goal in children aged 1-4 years because of the adverse effects on intellectual development. For individual children Council recommended a range of graduated responses depending on blood lead concentrations commencing at 15 µg/dL (education on ways to minimise exposure and reduce absorption and environmental assessment with remediation if appropriate).

Blood lead levels are only a reflection of a child's recent interaction with the environment and not a measure of total lead in a child's body. The level depends on the amount of lead a child absorbs through taking in dust, soil, paint, food, water, or other substances containing lead. Once absorbed, lead is distributed to bones, teeth, soft tissues, hair and other areas of the body. Blood lead levels provide a good indication of recent lead exposure (3 to 4 weeks) and teeth are an indicator of historical exposure. Analysis of lead in hair, while costly, is not a reliable indicator of past exposure, due to possible lead contamination on the outside of the hair, and the lack of long-term epidemiological studies to provide an interpretation of the results.

Which children should be tested?

Most children with lead poisoning show no symptoms unless the child has been recently exposed to very high levels of contamination (blood lead levels of 50 µg/dL).

Children who may be at risk of having elevated lead levels (without an obvious cause for concern) and whom one might consider measuring their lead levels include the following:-

• Children aged 12-48 months who live in or are frequent visitors to older dilapidated housing with peeling paint.
• Children aged 12-48 months who have been present during "unsafe" renovations of older housing (painted before 1970).
• Children with pica living in older housing with peeling paint and exposed soil.
• Children aged 12-48 months living near lead smelters, battery breaking yards, lead ore bodies, or on highways with heavy traffic.
• Children exposed to the less common exposure pathways eg. lead hobbies, folk medicines containing lead, etc.

Blood lead levels should be collected by a trained paediatric blood collector on venous blood using proper techniques and lead-free equipment.

The basic management of young children with elevated blood lead levels includes:

1. Identification and removal of the source of lead, or removal of the child from the source.
2. Improved nutrition and administration of iron supplements where appropriate to minimise lead absorption.
3. Education on ways of minimising lead exposure.
4. Chelation therapy when indicated.

What about school age children?

There is increasing evidence that exposure to lead during pre-school years may cause behavioural and learning disorders similar to children diagnosed with ADD (see "Can exposure to lead cause ADD?").

As most children diagnosed with ADD are of school age it is likely that their blood lead levels will be low (remember blood lead levels are only indicative of recent exposure). However, if they were exposed to lead during their first 3-4 years of life (i.e. when they are most at risk) lead would have accumulated in their bones and teeth. Therefore, by measuring dentine (tooth) lead we are able to determine whether children have been previously exposed.

If parents are interested in assessing whether their child has been exposed to lead during earlier life they need to:

1. Collect their child's two top front baby teeth (upper central incisors usually fallout between the ages 5-8). Other teeth may be measured but the results may not be as reliable;
2. Wrap the teeth in tissues then plastic to prevent damage during transport;
3. Enclose the teeth with details of the child's age, sex, your address and phone number and a history of the age and type of construction of the house the child resided in during his/her first four years, his/her play patterns (e.g. time inside versus outside), mouthing tendencies and any medical history, in an envelope.

As of June 2005, Lidcombe lab is now offering tooth lead testing to the public. The cost is $40 per tooth, aim is one week turnaround, there is no interpretive report, no identification of the tooth by a dentist and no guarantee that the lead is not on the outside of the tooth due to contamination in storage or transit. Samples can be delivered to the lab between 9-4:30 weekdays or posted to PO Box 162 Lidcombe 2141, Less than 10 samples will cost $40 each and if total is less than $100, a cheque made out to "Division of Analytical Laboratories" must accompany the samples. Larger amounts will be billed. The Lidcombe lab was used for tooth lead assays in the PhD thesis on lead in children's teeth in Broken Hill by Monish Arora.
DAL Lidcombe Lab, PO Box 162, Lidcombe NSW 1825 Australia PH dir 02 9646 0424, sw 02 9646 0222. WEB: http://www.health.nsw.gov.au/Pages/default.aspx

Institute of Clinical Pathology and Medical Research, NSW Health Dept - Division of Analytical Laboratories (DAL), part of Westmead AHS at Lidcombe.
NATA accredited to test lead in food residues, agricultural products, blood, serum, urine, water, children's toys and from buildings. Samples can be delivered to the lab between 9-4:30 weekdays or posted to PO Box 162 Lidcombe 2141.

Less than 10 samples will cost $40 each and if total is less than $100, a cheque made out to "Division of Analytical Laboratories" must accompany the samples. Larger amounts will be billed

The American Association for Clinical Chemistry publication: Directory of Rare Analyses, indicates that National Medical Services (NMS), performs lead testing in Hair, Nails and other specimens for post-mortem or forensic cases. NMS also offers tooth lead testing as a "Special Request" test. They do not however work with private individuals. A person would need to either go through a Dr., Lawyer or another lab in order for NMS to do the testing.
NMS, 2300 Stratford Avenue, Willow Grove, PA, 19090-4195 USA
PH: 2156574900 or free call USA 800-522-6671
EMAIL: nms@nmslab.com WEB: www.nmslab.com

Editor's notes:

Omnicare Medical Centre,
2 Brady St, Mosman, Sydney. Ph: (02) 9960 4133.