Impacts of carbofuran on birds in Canada and the United State - Carbofuran and Wildlife Poisoning: Global Perspectives and Forensic Approaches - page 237

Analysis of soil samples (unreported levels) indicated that the farmer had applied carbofuran at the
correct rate (British Columbia Ministry of Agriculture and Fisheries 1989; Whitehead 1989).
8.4.4.1.10 February 1995, alfalfa, Imperial County, California
Observers reported 61 dead American wigeon and one mallard in this incident (Fite, Randall, Young
et al. 2006). They had been grazing on the alfalfa. Positive residue determinations were obtained on
three birds.
8.4.4.1.11 June 1996, alfalfa, Modoc County, California
Fite, Randall, Young et al. (2006) report that six Canada geese were killed and 100 affected follow-
ing aerial application of the insecticide. Two gut content samples were measured at 0.4 and 1.5 ppm.
8.4.4.1.12 June 1997, alfalfa, Loudoun County, Virginia
Six Canada geese found dead at a reservoir had grazed in a nearby treated fi eld. Stomach contents
(it is not clear whether from a single bird or a pooled sample) contained 8.6 ppm carbofuran (Fite,
Randall, Young et al. 2006).
8.4.4.1.13 March 1999, alfalfa, San Bernardino County, California
Observers reported 40 dead American wigeon in this incident (Fite, Randall, Young et al. 2006).
Gastrointestinal tract contents ranged from 1.5 to 5.2 ppm carbofuran. Skin sampled from the foot of
birds ranged from < 0.05 to 4.1 ppm.
8.4.4.1.14 March 2000, alfalfa, Chaves County, New Mexico
Fite and colleagues (2006) report a very large kill of 1 200 snow geese ( Chen caerulescens ) in a fi eld
treated with 840 g ai/ha. They provide no further details.
Clearly, waterfowl species that graze on treated vegetation risk exposure even at the lower
registered rates of application. Other grazing species may also be at risk, although galliformes
(e.g., grouse or pheasant) may be less sensitive than waterfowl on the basis of the species tested
to date. In an unpublished Pesticide Informational Report of the CDFG, E. Littrell calculated that
alfalfa residue levels of 2 ppm could still be potentially lethal to American wigeon a species of
duck very prone to grazing in fi elds. Indeed, many of the values for gut contents reported in the inci-
dents described in Section 8.4.4.1 are below this level. Littrell based this assessment on food con-
sumption habits of waterfowl in alfalfa and on the LC 50 value of 79 ppm established in the 14 day old
mallard. On that basis, he proposed a 'safe re-entry interval' of seven days for waterfowl in sprayed
alfalfa fi elds. Residue levels in alfalfa associated with instances of mass mortality in California were
never higher than 44 ppm. Here, we caution the reader that the use of the LC 50 to assess avian risk
has largely been discredited. See Mineau, Jobin and Baril (1994).
8.4.4.2 Incidents where birds were killed by eating seeds or insects that were
contaminated with liquid carbofuran
Based on the species affected, it is clear that carbofuran applied in liquid form kills much more
than grazing species. In the following incidents, we surmise that the birds were feeding on wild or
crop seeds and/or insects contaminated by either a foliar or a ground spray of carbofuran. When the
governments of the United States and Canada severely restricted the legal uses of granular formula-
tions of carbofuran, farmers began applying the fl owable formulation directly to soil in increasing
numbers. Not surprisingly, the majority of the more recent kills have involved this type of use.
8.4.4.2.1 April 1986, tomatoes, Virginia
Field personnel found at least eight American goldfi nches ( Carduelis tristis ) near a tomato fi eld
sprayed with carbofuran. The birds' gizzard contents contained 0.17 ppm carbofuran. The birds