112
Pesticides, Organic Contaminants, and Pathogens in Air
In order to determine whether the uptake of pesticides in fog was unique
to the wintertime ground fog, or tule fog, of the inland Central Valley,
Schomburg et al. (1991) used a scaled-up tefon strand fog collector (Seiber
et al., 1993) to analyze air and fogwater in several spring advective oceanic
fogs collected near Monterey, CA, and the heavily agricultural Salinas Valley
and associated coastal plains. The pesticide content and distribution for
several pesticides common to both areas (chlorpyrifos, diazinon, etc.) were
remarkably similar between the coastal and Central Valley samples. The conversion of thion to oxon and the aqueous phase enrichments were also very
similar. The data also provided support for the hypothesis that nonflterable,
strongly sorptive particles and colloids in the fogwater cause the enhancement of pesticides in water in the foggy atmosphere.
Fogwater entrainment and concentration of chemicals are not unique to
pesticides. Sagebiel and Seiber (1993) analyzed wintertime fog and interstitial air from a community in the Central Valley during a time when residential wood burning occurred. Guaiacol, 4-methyl guaiacol, and syringol were
the most commonly found among the 16 methoxylated phenolic lignin combustion products confrmed by GC/MS in fog samples. The distribution of
methoxylated phenols generally followed Henry’s law, that is, did not show
the dramatic enrichments observed for less polar pesticides. This suggested
that enrichment is a function of analyte hydrophobicity rather than any special structural features. Concentrations of methoxylated phenols in fogwater
ranged to 1,408 µg/L for syringol, and generally were in the 1–100 µg/L range
when detected.
Seiber et al. (1993) provided more details on the distribution of pesticides
in air, fogwater, and plant surfaces in a series of experiments carried out at
the Kearney Agricultural Research Center at Parlier, CA. Fogwater contained
residues of the four OP dormant spray insecticides (parathion, chlorpyrifos,
diazinon, and methidathion) and their oxons (Table 7.3).
Concentrations ranged to 91 µg/L for parathion and 76 for diazinon and
were signifcantly lower for oxons (to 19 µg/L for paraoxon, 6.2 µg/L for
methidathion oxon, 3.4 µg/L for chlorpyrifos oxon, and 3.0 µg/L for diazinon
oxon), in fogwater sampled with the Tefon strand collector. When fogwater was collected by simply placing a collector beneath the drip lines of tree
canopies, similar water concentrations were observed, but the ratio of oxon
to thion increased dramatically for the four insecticides, to an average of 0.7
(diazinon) and 1.35 (methidathion) (Table 7.3). This indicated either that conversion of thion to oxon occurred in fogwater as it collected on, and passed
through the foliage, or that conversion of thion to oxon occurred in the tree
parts (leaves, needles, limbs) after the water evaporated as the fog lifted, with
the surface-formed oxon being removed during the next episode of fog. The
apparent tree surface catalysis of thion to oxon was noted previously (Spear
et al., 1975).
The phenomenon of enrichment of chemical solutes in the suspended aqueous phase of foggy atmosphere has been the subject of much discussion since
Pesticides, Organic Contaminants, and Pathogens in Air
In order to determine whether the uptake of pesticides in fog was unique
to the wintertime ground fog, or tule fog, of the inland Central Valley,
Schomburg et al. (1991) used a scaled-up tefon strand fog collector (Seiber
et al., 1993) to analyze air and fogwater in several spring advective oceanic
fogs collected near Monterey, CA, and the heavily agricultural Salinas Valley
and associated coastal plains. The pesticide content and distribution for
several pesticides common to both areas (chlorpyrifos, diazinon, etc.) were
remarkably similar between the coastal and Central Valley samples. The conversion of thion to oxon and the aqueous phase enrichments were also very
similar. The data also provided support for the hypothesis that nonflterable,
strongly sorptive particles and colloids in the fogwater cause the enhancement of pesticides in water in the foggy atmosphere.
Fogwater entrainment and concentration of chemicals are not unique to
pesticides. Sagebiel and Seiber (1993) analyzed wintertime fog and interstitial air from a community in the Central Valley during a time when residential wood burning occurred. Guaiacol, 4-methyl guaiacol, and syringol were
the most commonly found among the 16 methoxylated phenolic lignin combustion products confrmed by GC/MS in fog samples. The distribution of
methoxylated phenols generally followed Henry’s law, that is, did not show
the dramatic enrichments observed for less polar pesticides. This suggested
that enrichment is a function of analyte hydrophobicity rather than any special structural features. Concentrations of methoxylated phenols in fogwater
ranged to 1,408 µg/L for syringol, and generally were in the 1–100 µg/L range
when detected.
Seiber et al. (1993) provided more details on the distribution of pesticides
in air, fogwater, and plant surfaces in a series of experiments carried out at
the Kearney Agricultural Research Center at Parlier, CA. Fogwater contained
residues of the four OP dormant spray insecticides (parathion, chlorpyrifos,
diazinon, and methidathion) and their oxons (Table 7.3).
Concentrations ranged to 91 µg/L for parathion and 76 for diazinon and
were signifcantly lower for oxons (to 19 µg/L for paraoxon, 6.2 µg/L for
methidathion oxon, 3.4 µg/L for chlorpyrifos oxon, and 3.0 µg/L for diazinon
oxon), in fogwater sampled with the Tefon strand collector. When fogwater was collected by simply placing a collector beneath the drip lines of tree
canopies, similar water concentrations were observed, but the ratio of oxon
to thion increased dramatically for the four insecticides, to an average of 0.7
(diazinon) and 1.35 (methidathion) (Table 7.3). This indicated either that conversion of thion to oxon occurred in fogwater as it collected on, and passed
through the foliage, or that conversion of thion to oxon occurred in the tree
parts (leaves, needles, limbs) after the water evaporated as the fog lifted, with
the surface-formed oxon being removed during the next episode of fog. The
apparent tree surface catalysis of thion to oxon was noted previously (Spear
et al., 1975).
The phenomenon of enrichment of chemical solutes in the suspended aqueous phase of foggy atmosphere has been the subject of much discussion since