Environmental Engineering Reference
In-Depth Information
that the application was properly done; the birds were apparently consuming the seeds in the fur-
rows. Carcasses were reported to contain (unspecifi ed) carbofuran residues.
8.2.2.1.13
March 1992, corn, Brunswick County, North Carolina
Similarly, when a citizen reported 40 to 50 dead and disabled birds in her yard, which was adjacent to
a small (7 hectare) corn fi eld, investigators were called in (Augspurger, Smith, Meteyer et al. 1996).
Over the course of the next two days, they found another 23 birds including red-winged blackbirds,
eastern bluebirds (
Sialia sialis
), American robins, and an unidentifi ed fi nch. There also, they con-
cluded that the product had been used properly.
8.2.2.2 Kills associated with puddling of fi elds after application
Puddling in treated fi elds represents a different type of hazard inherent in carbofuran granules.
Typically, the farmer applies the granules at seeding. During the spring and summer, and even dur-
ing the following autumn and winter, puddles may form in the fi elds or the fi elds may even fl ood
completely. At that point, the fi elds become attractive foraging sites for waterfowl and other birds.
It is unlikely that waterfowl selectively pick up single granules from the soil surface. Rather, given
their body size and bill morphology, it is more likely that birds inadvertently ingest granules as they
sift through sediments or while ingesting contaminated water and crop residues. Dermal exposure
from contaminated puddles is also possible based on existing research which concluded that dermal
exposure from pesticide sprays was more important than dietary exposure (Driver, Ligotke, Van
Voris et al. 1991).
At issue is the length of time that a hazard remains after the application of the granules. Wilson and
colleagues (2002) verifi ed what had long been suspected, namely that under some fi eld conditions
(e.g., acidic soils with pH below 6) several granular insecticides were quite persistent. Carbofuran
was the most persistent, with half-lives of 129 and 97 days in silt loam and muck soils, respec-
tively. Base-catalysed hydrolysis is the most important chemical degradation pathway for carbofuran
(reviewed in NRCC 1979). The half-life of carbofuran in water due to hydrolysis alone ranged from
0.2 days at pH 9.5 to 1 700 days at pH 5.2. Some scientists have postulated that microbial action also
aids in breakdown of granular carbofuran in fl ooded soil situations, but this may only be the case if
the soils are neutral or alkaline (reviewed in Trotter, Kent and Wong 1989, and see Chapters 1 and 3).
Before the Wilson (2002) study reported above, Williams, Brown and Whitehead (1976) had
shown a buildup of residues in Fraser Valley (BC) soils (pH of 5.3 to 5.6) after two years of use.
Ahmad, Walgenbach, Sutter et al. (1979) calculated a half-life of 60 to 75 days for Furadan 10G and
11 to 13 days for the technical grade at pH 6.5. Caro, Freeman, Glotfelty et al. (1973) estimated
a 117 day half-life for a Furadan 10G formulation applied in-furrow in silt loam of pH 5.2. In a
kill incident reported below (in 8.2.2.2.2), 10G granules retained almost half of their initial carbo-
furan concentration seven to eight months after weathering in the fi elds. FMC (1976b) indicated
that granules still contained 6.33% carbofuran (the nominal concentration of Furadan 10G is 10%)
three months after exposure to soil from the Reifel Refuge in the Fraser Delta. It is therefore not
surprising that the kill record refl ects a long period of time between applications of the granules and
kills. Despite the known extreme persistence of carbofuran under acidic conditions, we are unaware
of any investigation into increased residue levels in agricultural produce as a result, although this
would seem warranted.
8.2.2.2.1
December 1973, turnip, Richmond, British Columbia
Investigators found between 50 and 60 dead northern pintails (
Anas acuta
) and mallards in a partly
fl ooded fi eld along the Fraser River. A water sample collected from a puddle and a soil sample con-
tained 1.7 and 1.96 ppm carbofuran, respectively (Whitehead 1975a).
Search WWH ::
Custom Search