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lead shot for in vitro gastrointestinal simulation experiments.
They found that far more lead in the cooked gamebird meat
was bioaccessible (soluble and available for absorption) in the
simulated intestine phase when a recipe containing vinegar
was used (6.75%) than when wine was used (4.51%) or than
in uncooked partridge meat (0.7%). However, the reliability of
estimates from in vitrogastrointestinal simulation experiments
depends upon the uncertain degree to which the experiment
mimics human digestion and absorption (Zia et al. 2011), and
frequently-used cooking methods may vary between countries.
Because of these potential problems with in vitro estimates,
Green and Pain (2012) used observations from two studies of
Greenland adults (Bjerregaard et al. 2004, Johansen et al. 2006)
to derive a quantitative empirical relationship between the
mean daily intake of dietary lead from the meat of birds killed
using lead shot and the mean concentration of B-Pb. There
was a strong relationship in the data from both Greenland
studies between mean B-Pb and the estimated mean rate of
intake of dietary lead frommeals of cooked wild bird meat. The
regression models of Green and Pain (2012) indicated that the
effect of ingested ammunition-derived lead on B-Pb was 39%
lower than that expected for lead not derived from ammunition
(Carlisle and Wade 1992). However, it should be noted that this
regression method is subject to a known bias. Least squares
regression assumes that the independent variable (in this case
the dietary lead intake rate) is known without error. This is not
the case because the intake rate means used were determined
from sample estimates with attached errors which cannot be
fully quantified and adjusted for. The direction of this bias on
the slope of the fitted regression is negative, meaning that the
true absolute bioavailability of lead may be larger than that
estimated by this method.
There appear to be no published studies in which B-Pb was
related to ingestion ratesof ammunition-derived lead inchildren.
The bioavailability of lead in the ordinary diet is considerably
higher in children than in adults (Mushak 1998, IEUBK 2010).
Green and Pain (2012) assumed that the ratio of the absolute
bioavailability of dietary lead from cooked wild bird meat to
that of lead from the ordinary diet, calculated for adults (above),
would be the same in children. As there is awidely-used value for
the absolute bioavailability to children of lead from the ordinary
diet (0.5, fromMushak 1998, IEUBK 2010), they estimated a value
for absolute bioavailability in children of dietary lead derived
from the cooked meat of wild birds of 0.3060. The same caveat
about probable negative bias in this estimate applies as that
described above for adults.
Effects of lead on human health
and functioning
The consequences of exposure to lead for human health
have been considered in great detail by the appropriate
authorities of several countries. Lead affects the nervous,
urinary, cardiovascular, immune, reproductive and other body
systems and a range of organs, including the brain (USATSDR
2007, EFSA 2010). Experiments show that high doses of lead
can induce tumours in rodents, and possibly humans, and the
International Agency for Research on Cancer classified inorganic
lead as ‘probably carcinogenic to humans’ (Group 2A) in 2006
(IARC 2006). Body systems particularly sensitive to low levels
of exposure to lead include the haematopoietic, nervous,
cardiovascular and renal systems (EFSA 2010).
Once lead has been absorbed into the body, its effects on
health and functioning are largely independent of its original
source. Hence, correlations between health outcomes and
concentration of lead in tissues are an important source of
information on effects of lead on health. The concentration
of lead in whole blood is the most widely used measure of
recent exposure, because of the short half-life of lead in the
blood. Although measurements of lead concentrations in other
tissues, such as bone, might be more informative about long-
term exposure and chronic effects on health, sampling them is
impractical and seldom possible. Hence, much of what is known
about the health effects of lead is based upon correlations
between health outcomes and B-Pb.
As evidence about the health effects of lead has accumulated
and the sensitivityof analyses has increased, B-Pbconcentrations
shown to be associated with human health effects have
correspondingly decreased. In addition, as human health
concerns have resulted in regulations that have reduced human
exposure from several previously important sources, such as
occupational exposure, plumbing, paint and petrol additives, it
has become possible to detect significant associations between
health outcomes and B-Pb at much lower concentrations than
would previously have been possible. Consequently, there
has been a progressive decrease in the B-Pb concentrations
proposed as thresholds for action and these are now one sixth
or less of those considered as protective of human health in the
Rhys E. Green & Deborah J. Pain