Environmental Engineering Reference
In-Depth Information
derivatives (pyrethroids) have been developed which have greater environ-
mental stability and higher biological activity. Pyrethroids have very low
vapor pressures and are classified as nonvolatile chemicals. Pyrethroids
include permethrin, deltamethrin, cypermethrin, cyflutrin, resmethrin,
teliomethrin, and alletrin. Of these, permethrin is the most widely used. The
pyrethroids are often formulated with piperonyl butoxide (PBO) which acts
as a synergist to enhance their biological activity. Synergists reduce the rate
of pyrethroid degradation after uptake by insects.
Pyrethroids are increasingly being used indoors for a variety of insect
pest applications, including flea and cockroach control. They are replacing
such compounds as chlorpyrifos, diazinon, and dichlorvos. Their use is
expected to increase significantly as a result of the regulatory phaseout of
chlorpyrifos applications indoors and for termiticidal treatments.
D. Indoor exposures and levels
1. Biocides
In the late 1980s, staff from the Centers for Disease Control (CDC) conducted
an investigation of a 4-year-old child who was diagnosed with acrodynia (a
relatively rare form of childhood mercury poisoning) after the child's home
was painted with 12 gallons of interior latex paint containing 930 to
950 mg/L mercury. CDC staff concluded that the child had been poisoned
by inhalation of mercury vapors from phenylmercuric acetate (PMA), one
of the most commonly used mercury biocides in latex paint.
In response to this incident, CDC and other investigators measured
elemental mercury levels in 21 residences that had been painted 3 months
earlier with a mercury-containing paint and 16 control residences (not
recently painted). The median air concentration in exposed homes was 0.3
µ
g/m
3
, with a range from below the limit of detection (BLD) to 1.5
µ
g/m
3
;
unexposed homes had a BLD median level, with a range of BLD to 0.3
µ
g/m
3
.
Six of the exposed homes had mercury levels >0.5
g/m
3
, the guideline limit
for acceptable indoor air levels recommended by the Agency for Toxic Sub-
stances and Disease Registry (ATSDR).
Mercury emission studies of 13 paints containing mercury biocides such
as PMA, diphenyl mercury, dodecenyl mercury succinate, diphenyl mercury,
phenyl mercuric oleate, and chloromethoxy propyl mercuric acetate, indicate
that though biocides are organic mercury compounds, emissions are in the
form of elemental mercury which, because of its high vapor pressure, readily
becomes airborne.
Airborne mercury sorbs on household dust and materials such as carpet.
As would be expected, higher dust mercury levels are found in homes
recently painted with mercury-containing paints. Medians and ranges of
mercury levels in house dust in a sample of exposed and “unexposed” U.S.
homes were 3.76 mg/kg, 0.93 to 11.91 mg/kg, and 1.78 mg/kg, 1.0 to 4.8
mg/kg, respectively. It appears that mercury contamination of floor dust in
U.S. homes is common; it may pose an exposure risk to small children.
µ
