Absorption - Pesticide Biotransformation and Disposition - page 34

the need to evaluate the influence of current and novel inerts on the toxicology and
dermal absorption of active ingredients in pesticide formulations.
Several studies have demonstrated the penetration-enhancing ability of acetone
compared to water, ethanol, or other vehicles commonly used in dermal absorption
studies. Early work by O'Brien and Dannelley (1965) showed that in comparison with
benzene and corn oil, acetone was best at enhancing carbaryl absorption. More recent
studies have also demonstrated the enhancing effect of acetone compared with other
solvent systems on the absorption of carbaryl, p -nitrophenol, and 2,4-D ( Baynes and
Riviere, 1998; Brooks and Riviere, 1995; Moody et al., 1992 ).
However, other studies have demonstrated that commercial formulations are more
effective than acetone at enhancing pesticide absorption. Methyl parathion absorption
in vitro in human skin at 24 h was 1.3% in acetone, but was significantly increased
to 5.2% in a commercial formulation ( Sartorelli et al., 1997 ). Likewise, in vivo der-
mal exposure studies of lindane in humans resulted in approximately 60% with a
white spirit formulation and 5% with an acetone vehicle ( Dick et al., 1997a,b ). In
these experiments, more of the lindane dose (79%) remained on the skin surface at
6 h with acetone than with the white spirit formulation (10.5%), and significant lev-
els of lindane accumulated in the stratum corneum with white spirit (30%) and with
acetone (14.3%) at 6 h. These findings strongly suggest that the white spirit formulation
enhanced lindane penetration with respect to the acetone vehicle. The in vitro stud-
ies with human skin also demonstrated a similar pattern, although only 18 and 0.3%
of the dose was absorbed into the perfusate at 6 h using the white spirit formulation
and the acetone vehicle, respectively. Topical application of 1% commercial lotion of
lindane in vitro in human and guinea pig skin resulted in absorption levels as high as
71.72 and 35.31%, respectively, at 48-h exposure ( Franz et al., 1996 ).
Dermal absorption of alachlor as an emulsifiable concentrate and microencapsulated
formulation was demonstrated to be 8.5 and 3.8%, respectively, in rhesus monkeys after
a 12-h exposure ( Kronenberg et al., 1988 ). About 88% of the systemically absorbed
dose was excreted in urine within 48 h. However, the differences between these two
formulations were not statistically significant. Although dilution of either of these for-
mulations (1:29) slightly enhanced alachlor absorption, these effects were surprisingly
not statistically significant. One in vitro study with human skin demonstrated similar
absorption data (0.5-4%) after an 8-h exposure and peak fluxes within 3-5 h postappli-
cation ( Bucks et al., 1989b ). However, a significant effect of formulation dilution with
water was observed in this study, even though the same mass of alachlor was applied to
skin. Not surprisingly, a greater fraction of alachlor was present on the skin surface and
skin tissue than in the receptor fluid, and the high capacity for stratum corneum bind-
ing demonstrated in this study is not unique for related chlorinated aromatic chemicals.
Data from several studies have demonstrated that pesticide applicators may be at
risk of increased dermal absorption of some pesticides if they apply sunscreen or an