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So much first-class information has been presented during the
symposium that I cannot attempt to summarise it all, but what
I would like to do is pick out what I think are the main issues
to emerge:
Lead must now be one of the most thoroughly and extensively
studied of anthropogenic toxins. At this symposium, we have
heard only parts of the evidence available on its biological
impacts, mostly relating to the UK; when added to findings from
the rest of the world, we have a huge body of scientific evidence,
which is consistent and overwhelming in its messages. In what
I have to say now, I will rely mainly (but not entirely) on this
current symposium.
Effects on people
Toxic effects of lead on people have been recognised for
centuries (Stroud 2015). It is a non-essential component of
the diet which, at very low levels, affects multiple physiological
systems, including nervous, renal, cardiovascular, immune and
reproductive systems. It also affects the behaviour of animals,
and has been implicated in the criminal behaviour of some
people. Influential medical publications have listed lead as
‘probably carcinogenic’.
Owing to this knowledge, most important sources of lead in
the environment of the UK have already been significantly
reduced or eliminated (paints, gasoline, lead-pipes etc.), while
other remaining uses (as in batteries or lead-sheeting) are well
controlled. This leaves lead-based ammunition as the remaining
greatest source of emissions of lead to the environment that
remains largely unregulated. An estimated 5,000 tonnes of lead
ammunition are deposited on the UK every year, raising existing
environmental levels, especially in areas of concentrated
shooting activity (Painet al. 2015).
Since additives to petrol were regulated, the main source of lead
contamination of people has been via the diet, that derived from
lead ammunition is the most readily controllable source. Lead
obtained from wild meat, whether in the form of shot pellets or
bullet fragments, has been linked with elevated blood levels in
people, such blood levels tending to increase linearly with the
amounts of game meat consumed. Links between the use of
lead ammunition and lead in the human body, and between
lead in the body and human health and well-being are now
firmly established by several independent studies (e.g.see Green
and Pain 2015, Knutson et al. 2015).
In recent years, leadhas been shown to affect adults and children
at far lower concentrations in body tissues than formerly
thought, and at lower concentrations than current regulations
acknowledge (although acceptable levels have been reduced
over the years (Green and Pain 2015)). There is no level of lead
exposure in children or adults known to be without deleterious
effects. In other words, there is no toxicity threshold: the concept
of a ‘safe level’ is redundant. Exposure in childhood to even
slightly elevated levels of lead produces measurable and lasting
neurological deficits in intelligence and behaviour. Neonates
and children with growing brains are especially susceptible.
Relatively new findings concern the behaviour of bullets and
shot: the way that lead-based ammunition leaves behind
tiny fragments on passage through an animal. These can be
distributed widely within carcasses, including places distant
from thewound tract.Thismakes it almost impossible for people
to avoid ingesting lead along with meat. The bits of lead are so
small and scattered that no normal butchery can remove them.
So the consumption of lead-killedmeat almost inevitably results
in the consumption of undetected lead.While this fact may have
been known to some for years, new studies have re-emphasised
it in a most dramatic way, for example from X-ray images of
shot animals (Green and Pain 2015, Gremse and Reiger 2015).
OXFORD LEAD SYMPOSIUM:
CLOSING REMARKS
Professor Ian Newton OBE, FRS, FRSE