Blood test results show elevated lead levels in some Waikouaiti, Karitane, and Hawksbury residents, including children.
The tests were conducted after the highly poisonous heavy metal was found to be 39 times the acceptable limit in a
drinking water sample. Health authorities have not revealed the number of people with elevated blood lead levels, and
are conducting further investigations to find out if it is linked to the drinking water, or if other factors could also
be at play.
The SMC asked experts to comment.
Malcolm Tingle, Associate Professor of Toxicology, Department of Pharmacology and Clinical Pharmacology, University of
Auckland, comments:
“Lead can be absorbed from diet, including drinking water. It is absorbed more efficiently in children than adults, and
it is influenced by other dietary factors. For example, its absorption increases when intake of iron or calcium (present
in dairy products) is low. Because lead is cleared from the body slowly by the kidneys, it accumulates if intake is too
great, and can distribute from the blood into soft tissues, such as the liver, and into bone, where it can remain for
many years. These processes are factored in when setting safe exposure levels such as those in drinking water.
“Lead has no biological function and is toxic to most living things. In humans, lead is associated with several adverse
effects. Of particular concern is high exposure in young children that may cause in neurological problems, often
detected as learning difficulties and decreased IQ. There is a weaker association with lead exposure and
Attention-Deficit/Hyperactivity Disorder (ADHD). In adults, it is also more likely to increase blood pressure, decrease
the lifespan of the red blood cells, and/or cause kidney toxicity.
“Whilst it is accepted that there is no safe concentration of lead in the blood (because it has no benefit to health),
it must be kept in mind that the studies into the effects of lead on outcomes like learning difficulties and ADHD have
studied children who have had long-term (perhaps even lifetime) exposure to lead (for example, living near lead
smelters) and so the blood concentration is likely in equilibrium with concentrations in soft tissues and bone. The
current contamination has clearly resulted in lead being detected in blood of some individuals, which is concerning, but
there is a lack of data on the effects of relatively short-term exposure to lead on neurological outcomes. There is also
a lack of studies investigating how quickly blood levels will decrease to safe levels under such circumstances.”
No conflict of interest.
Professor Sally Gaw, Director of Environmental Science, School of Physical and Chemical Sciences, University of
Canterbury, comments:
“Despite the toxicity of lead being known over the centuries, New Zealanders continue to be exposed to it. Any survey of
blood lead levels in the community is likely to identify people with levels above acceptable guidelines because of the
prevalence of lead. The current drinking water issue in Waikouaiti, Karitane and Hawksbury has highlighted the legacy of
using lead-containing materials in the joints of old cast iron water pipes.
“Alongside drinking water pipes, there are a range of other potential sources of lead in people’s homes that will
contribute to the amount of lead in their bodies. These include lead in tapware, lead in crockery glazes especially
pre-1980s crockery, and hobbies that use lead such as lead-lighting of glass, preparation and use of ammunition
containing lead, and melting lead to prepare fishing weights (definitely not recommended).
“The most common source of lead exposure in New Zealand is lead-based paint, which was widely used on buildings in New
Zealand until 1965 and people should assume that houses built before 1980 are likely to contain lead-based paint. People
are exposed to lead-based paint when it flakes off, during incorrectly managed home renovations, as well as burning
timber painted with lead-based paint.
“Children are particularly at risk of lead exposure both because of its toxic effects on the developing brain but also
because they tend to have higher exposure to lead in dust due to spending more time on the floor and younger children
are more likely to stick things in their mouth or chew non-food items.”
No conflict of interest.
Dr Nick Kim, Senior Lecturer, Subject Leader – Environmental Health, School of Health Sciences, Massey University,
comments:
“The rush to undertake blood lead testing was always going to lead to this situation where a number of samples would
come back with positive results, and a handful would be above a health guideline value.
“Lead occurs naturally and there’s always a baseline intake from food, so we all have a natural intake of daily lead.
Whether that is at levels that are detectable in blood will vary both with the type of foods a child eats and the
sensitivity of the analytical technique.
“After that, we have range of potential sources where the two most prominent are dust contamination from (usually old)
lead paint, and the legacy of leaded petrol in urban garden soils. Lead paint is associated with many older weatherboard
houses, both on the boards and in the soil. As an example, children using a playground near an old school building or
early childhood centre (e.g. converted old villa) could experience higher exposures.
“Soil of urban areas show broadly elevated lead levels from the extended era when lead additives were used in New
Zealand petrol, and within that there’s gradient with the highest levels in gardens nearest to the busiest roads.
“Drinking water can of course sometimes be a source. Most often this is linked with to the individual plumbing to that
particular house. A work-around for that problem is to let water run for half a minute in the morning. We have also
previously found elevated lead levels in roof water.
“Outside of those, children could also be exposed from chewing or sucking on some types of toys, paints, and a range of
other idiosyncratic sources – such as a parent melting old lead-acid batteries down to make fishing sinkers, which has
happened.
“Without careful control sampling, blood testing will do nothing to clarify the source or sources of lead, and in this
case, whether there may have been a significant contribution to children’s lead intakes from their drinking water. With
pipes being replaced, I expect that this question will never be answered.”
No conflict of interest declared.