Guidelines for Metals and Metalloids in Ambient ... - ARCHIVE: Defra

Expert Panel on Air Quality Standards
is also applied, based on sensitisation as one of the critical health
effects.
159. The American Conference of Governmental Industrial Hygienists
(ACGIH) Threshold Limit Value (TLV), a concentration to which
nearly all workers may be repeatedly exposed over a working lifetime
without adverse effect), is 1.5 mg/m 3 for elemental nickel, 0.1 mg/m 3 for
soluble inorganic compounds, 0.2 mg/m 3 for insoluble compounds and
0.1 mg/m 3 for nickel subsulphide (all as 8 hour averages).
3.5 Justification for air quality guideline
160. The major health effect from exposure to nickel compounds by
inhalation is toxicity to the respiratory tract, including lung and nasal
cancer, although the latter is probably confined to occupational
exposures. The exact agent responsible for this effect remains
controversial. Animal experiments have implicated insoluble salts,
especially the subsulphide and the oxide, and these are certainly more
potent carcinogens than the soluble salts. Nickel sulphate (soluble) did
not increase lung cancer incidence in animals. However, more recent
epidemiological studies have indicated that soluble nickel salts may
contribute to the incidence of lung cancer in refinery workers (Grimsrud
et al., 2002). Sensitisation may result from inhalation of nickel salts, at
least from occupational exposure, but it is relatively rare. There are
insufficient data to allow a guideline value to be set for this response, but
the panel was not aware of any confirmed reports of sensitisation from
environmental exposure. Recent work with airborne particulate matter
in mice may indicate effects at lower levels of exposure (approximately
0.1 µg/m 3 ) but there are insufficient data to attribute these unequivocally
to nickel or to assess the impact on humans.
161. From the rat studies it can be concluded that the NOAEL for
exposures to the insoluble salts (oxide and subsulphide) is at least 0.11
mg/m 3 (NTP, 1996a,c). In the case of exposures to nickel sulphate (as
hexahydrate) chronic active inflammation and fibrosis was seen at 0.06
mg/m 3 and above (NTP, 1996b). Female (but not male) mice also
showed clear evidence of chronic inflammation at 0.06 mg/m 3 , the
lowest dose tested (NTP, 1996b). Thus, 0.06 mg/m 3 can be considered
to be the lowest adverse effect level (LOAEL) for soluble nickel
compounds in experimental animals.
162. It is evident from studies in vitro that soluble nickel salts may have
weak mutagenic potential and that this is probably due to the nickel
ion. There are no robust data to indicate whether this potential is
expressed in vivo. There is no substantial evidence for mutagenic
potential of the less soluble salts. It is therefore plausible that a
non-genotoxic mechanism, based on the formation of oxygen radicals
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