Risk Assessment - Toxicology of Metals - page 293

These recommendations and guidelines are set
based on risk assessments using predetermined safety
(or uncertainty) factors, and they are thus considered
health based, not considering other factors that may
be of importance when setting standards in national
legislation (see later).
Sometimes the precautionary principle is used when
issuing exposure recommendations (cf Hayes, 2005).
This principle may imply recommendation of volun-
tary limiting action against exposures to levels lower
that those otherwise recommended based on generally
agreed principles of risk assessment. Such lowering of
exposures is performed when it can be achieved with-
out any major costs. The precautionary principle is a
part of environmental legislation in Sweden and sev-
eral other European countries. This principle is related
to ethical considerations like the paragon of virtue
practiced by the ancient authorities in medicine like
Hippocrates.
Nongovernmental organizations like the Interna-
tional Commission on Occupational Health (ICOH)
sometimes issue policy documents of a precaution-
ary nature. For example, the ICOH Scientifi c Commit-
tee on the Toxicology of Metals in collaboration with
the Scientifi c Committee on Neurotoxicology recently
launched the “Declaration of Brescia,” recommending
lowering of limit values of lead manganese and mer-
cury and other preventive measures (Landrigan et al .,
2006 and Chapter 16).
Standards (national legislation) for occupational
exposures in the United States of America are set by
the Occupational Safety and Health Administration
(OSHA) and the National Institute for Occupational
Safety and Health (NIOSH). There are also drinking
water standards and air pollution standards in the
United States, which are set by the U.S. Environmen-
tal Protection Agency (USEPA) for a number of metals
such as lead and metalloids such as arsenic.
For cancer, the USEPA (USEPA/IRIS, 2006a,b) has
developed the unit risk concept, which is defi ned as
the upper bound lifetime cancer risk estimated to result
from an agent at a concentration of 1

the probability of a person developing cancer from
such exposures.
The EU has issued a limited number of permis-
sible occupational limits (PEL) that are either indica-
tive or binding for member states. They are based on
criteria documents issued by the Scientifi c Committee
on Occupational Exposure Limits (SCOEL). Mem-
ber states like Germany and Sweden have issued a
larger number of such limits that are implemented on
a national level in harmony with the PELs issued by
EU. Other countries like Japan, Russia, and China have
their own lists of permissible occupational exposure
limits. In the past, there were considerable differences
in such limits among countries like the Soviet Union
and China on the one hand and the United States and
western European countries on the other hand. As a
result of the International Program on Chemical Safety,
and its predecessors, starting in the 1970s, these differ-
ences have gradually decreased (see also discussion by
L Friberg in Chapter 1 of this handbook).
The European Union has regulated maximum lev-
els of contaminants, including lead, cadmium, and
mercury in foodstuffs (EG466/2001). The EU (1998)
has (98/83/EC) adopted drinking water standards for
a number of substances including some metals, and
these standards are implemented in member states
that report values to the European commission.
Biological exposure levels for metals/metalloids in
media such as blood for metals such as lead and urine
for arsenic are used in both occupational and envi-
ronmental exposure situations to assess the degree
of actual uptake into exposed individuals or popula-
tions. These data have been used as screening levels
for determining the need for medical interventions
or clean up activities. Blood lead measures for occu-
pational and childhood exposures would be the most
well-documented and extensively used example. In the
United States, the CDC has recommended a blood lead
level of concern for lead of 100

g/L; this level should
be used for screening of children.
In Sweden, biological exposure levels in terms of
blood concentrations allowed among industrial work-
ers are issued by the Swedish Work Environment
Authority (concerning levels for lead see Chapter 31
and for cadmium see Chapter 23).
When national or union authorities issue recom-
mendations and limits, a number of factors are taken
into consideration in addition to the risk characteriza-
tion such as socioeconomic, political, risk/benefi t, and
cost/benefi t factors (cf IPCS/WHO, 1999).
Readers of this handbook will see that the informa-
tion available on the toxicology of metals and their com-
pounds vary widely among metals. Only for a limited
number of the metals is there adequate information to

µ

µ g/L in water or

1 g/m 3 in air. The upper bound confi dence limit (UCL)

is defi ned as the upper bound of a confi dence interval
around any calculated statistic that is most commonly
an average. The interpretation of unit risk would be
as follows: unit risk = 2 × 10 −6 /

µ

g/L would indicate
two excess cancer cases (upper bound estimate) to be
expected per 1 million persons if exposed daily over a
lifetime to 1

µ

g of the agent per liter of water or cubic
meter of air. For cadmium, which the USEPA consid-
ers to be a class B1 carcinogen, the inhalation unit risk
estimate is 1.8 × 10 −3 (

µ

g/m 3 ) −1 . The USEPA uses math-
ematical models, based on animal studies, to estimate

µ