No. 104 - Miljøstyrelsen

44
A LOAEL of 0.025 mg Hg/m 3
(25 µg/m 3
) has been established in the working
environment for a normal workday/week. Corrected for permanent exposure 9
(from working environment to normal population) the LOAEL became 0.009
mg Hg/m 3
(9 µg Hg/m 3
). This value has been used by USEPA (together with
a certainty factor of 30 for particular sensitivity for children, variation between
individuals and for sensitivity of nervous system under development) to set a
reference concentration (RfC) for mercury vapours of 0.0003 mg/m 3 (0.3
µg/m 3 ). CalEPA used a further certainty factor of 10 since the basis was a
LOAEL, not a NOAEL, and arrived at a long-term limit value of 0.00003 mg
Hg/m 3 or 0.03 µg Hg/m 3 . CalEPA has furthermore set a limit value of 0.0018
mg/m 3 or 1.8 µg Hg/m 3 for a one hour exposure.
Agency for Toxic Substances Disease Registry (ATSDR) has set a minimum
risk level (MRL) of 0.0002 mg Hg/m 3 (0.2 µg Hg/m 3 ) and recommends
concentration limits after cleaning outdoors and spillage indoors of 0.03 and
0.001 mg Hg/m 3 respectively (i.e. 30 and 1 µg Hg/m 3 respectively).
A Canadian assessment uses a LOAEL value of 0.006 mg Hg/m 3 (6 µg
Hg/m 3
) and a certainty factor of 100, setting a long-term exposure limit of
0.00006 mg Hg/m 3 (0.006 µg Hg/m 3 ).
9
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