Environmental Engineering Reference
In-Depth Information
Organomercurials as Fungicides on Seed Grain
and in Latex Paint
Health Service to ban the use of mercury in fur felting in
1941 (Goldwater, 1972).
Occupational exposure to mercury today can occur
in a number of industries. Mercury vapor can be pres-
ent during the manufacture of chlor-alkali compounds
(i.e., caustic soda and chlorine), fl uorescent lighting, and
mercury-containing devices. It is released when elemen-
tal mercury is added to fi nely ground gold-containing ore
and then burned off to obtain pure gold. In low-income
communities that rely on gold mining for their livelihood,
children as young as 8 years old participate in this rudi-
mentary extraction method (Bose-O'Reilly et al., 2008).
Mining or smelting of mercury-containing ore can pose
exposure hazards as well (Feng and Qiu, 2008). Dentists
and their staff may be exposed when working with mer-
cury amalgams. Handling of mercury-contaminated waste
and demolition of buildings that have used fl uorescent or
high-intensity discharge lamps represent additional poten-
tial for exposure.
Mercury spills generally involve the release of elemen-
tal mercury (Zeitz et al., 2002). They can occur when a
mercury-containing object or device breaks. Breakages
of household thermometers have been relatively com-
mon, typically involving release of approximately 1 g of
mercury. Larger releases have been associated with break-
age of meters and gauges, such as those used to measure
blood pressure, and removal of mercury-containing gas-
pressure regulators, which were used with older gas meters
in homes (Hryhorczuk et al., 2006). In several instances,
elemental mercury spills have been discovered in resi-
dential buildings (as well as a day care center) that were
converted from industrial buildings in which mercury was
used (e.g., thermometer and mercury vapor lamp manu-
facturing) (Lee et al., 2009). Mercury spills may also occur
when children—attracted to the unusual appearance of
the metal—discover an unsecured store and share it with
friends, unknowingly contaminating their home or school
environment (Lee et al., 2009). When spilled, elemental
mercury can persist in a school, work, or home environ-
ment for many years if it is not removed properly (Carpi
and Chen, 2001).
Elemental mercury is not readily absorbed across the skin
or gastrointestinal tract, so ingestion or dermal exposure
rarely results in poisoning. However, because elemental
mercury can volatilize, and the vapor is readily absorbed,
there have been instances of acrodynia and neurologic dis-
turbances resulting from handling or playing with it (CDC,
1991; Risher et al., 2003; Abbaslou and Zaman, 2006).
Attempts to vacuum a spill have resulted in high expo-
sures due to enhanced volatilization (Baughman, 2006).
Cleaning up releases of elemental mercury can be straight-
forward in the case of small items such as a household
thermometer (US EPA, 2008b), but large spills can be very
expensive to clean up (Zeitz et al., 2002). The way the spill is
handled is an important determinant of ensuing exposure
in a community.
Organomercurials were used to preserve seed grain begin-
ning in the early 20th century, after these compounds were
determined to have antimicrobial properties (Goldwater,
1972). Such use was banned as a result of several incidents
of widespread poisoning that occurred when treated grain
was inadvertently ingested directly. The 1971-1972 Iraqi
epidemic involving exposure to methylmercury was cata-
strophic, with thousands admitted to the hospital and hun-
dreds dying (Bakir et al., 1973). Treated seed grain had been
imported from Mexico and distributed to farmers and their
families in the fall of 1971. The seed sacks were labeled, but
the warnings were in Spanish, and they used an unfamiliar
skull and crossbones symbol. The grain was colored with a
red dye, but this could be removed by washing, which gave
the false impression that the poison could also be removed.
Because the grain arrived at the end of the planting season,
families used it to prepare bread directly, thereby ingesting
poisonous amounts of methylmercury.
The Iraqi epidemic differed from Minamata in that
extremely high levels of exposure occurred over a shorter
period (several months). Maternal hair mercury concentra-
tion reached almost 700 ppm (infant blood levels were over
4000 µg/L within 2 months after delivery) (Marsh et al. 1987).
Similar to the Minamata incident, children exposed prena-
tally suffered more severe and permanent neurologic damage
than mothers (Amin-Zaki et al. 1979). Other incidents involv-
ing accidental ingestion of treated grain on a smaller scale had
occurred previously in Iraq and also in Pakistan, Guatemala,
and several other countries (Bakir et al. 1973).
Organomercurials were also used for their antimicrobial
properties in the latex paint manufacturing industry. Since
the early 20th century, manufacturers sometimes added phen-
ylmercuric acetate to latex paint to prevent the growth of mil-
dew and bacteria (Goldwater, 1972). It has been shown that
mercury levels are higher in homes where mercury-containing
paint has recently been applied (Agocs et al. 1990; Beusterien
et al., 1991), and on several occasions, children have been poi-
soned by the mercury vapor (Hirschman et al., 1963; CDC,
1990). In 1989, acrodynia and neurologic symptoms devel-
oped in a 4-year-old within a month of exposure in an unven-
tilated, newly painted home (CDC, 1990). His urine mercury
level was 65 µg/L. The indoor paint contained over 900 ppm
mercury, which was substantially over the 300 ppm limit
recommended by the EPA at the time. The EPA subsequently
banned use of mercury in interior paint, and its use in exterior
paint has been discontinued in the United States as well.
Derivation of Exposure Guidelines
for Methylmercury
The severity of neurologic damage that can result from
ingesting methylmercury—demonstrated by the poison-
ings that occurred in Japan and Iraq—has led governmental
