No. 104 - Miljøstyrelsen

LOAEL corresponds to the Danish occupational threshold limit value
mentioned above. Corrected for long-term exposure 8
(from working
environment to normal population) the LOAEL becomes 0.009 mg Hg/m 3
(9
µg Hg/m 3
). These values are based on adverse effects such as tremor and
memory loss.
Agency for Toxic Substances Disease Registry (ATSDR) set in 1999 a
minimum risk level (MRL) of 0.0002 mg Hg/m 3 (0,2 µg Hg/m 3 ). In addition,
TSDR has recommended concentration limits after cleaning and spillage
indoors (ATSDR, 1999).
In 2005 EPA in California established a long-term Reference Exposure Level
(REL) of 0.00003 mg Hg/m 3 (0.03 µg Hg/m 3 ) on the basis of a LOAEL of
0.025 mg Hg/m 3 (25 µg Hg/m 3 ) in the working environment (OEHHA,
2008). An adjustment to normal population exposure gave a LOAEL of
0.009 mg Hg/m 3 (9 µg Hg/m 3 ) (corresponds to USEPA above). This was
converted to REL by using larger (un)certainty factors than those used by
USEPA:
� An (un)certainty factor of 10, due to the fact that it is not a NOAEL,
� An (un)certainty factor of 30 for particular sensitivity of children,
variation between individuals and for sensitivity of nervous system
under development.
CalEPA has furthermore set a limit value of 0.0018 mg/m 3
exposure of one hour (Groth, 2008).
(1.8 µg/m 3
) for an
A new Canadian assessment assumes a LOAEL value of 0.006 mg Hg/m 3 (6
µg Hg/m 3 ). With an (un)certainty factor of 100 for uncertainty and modifying
factors the result is a REL of 0.00006 mg Hg/m 3 (0,06 µg Hg/m 3 )
(Richardson et al., 2009).
A summary of information about limit values long-term mercury exposure is
given in Table 4-2.
8
I.e. multiplied by a factor 5/7 to take into account all seven days of the week and not
only five workdays, and a factor 10/20 to take into account a respiratory volume of 10
for a workday and 20 m 3
for 24 hours.
m 3
41