Illnesses related to shank application of metam-sodium, Arvin, California, July 2002.

OBJECTIVES

To evaluate the health effects of methyl isothiocyanate (MITC) and other byproducts resulting from the soil-incorporated (shank) application of 25,000 pounds of metam-sodium on July 8, 2002, near the community of Arvin, California.

METHODS

Residents in a four-block area were interviewed regarding eye and upper respiratory irritation, non-specific systemic symptoms, and lower respiratory complaints. The distribution of cases was compared to results of Industrial Source Complex (ISC3) air dispersion modeling for the metam-sodium byproduct, methyl isothiocyanate (MITC). The 1-hour 200 ppb no-observed-effect- level (NOEL) and 800 ppb lowest-observed-effect level (LOEL) from a previous human eye irritation study were used to interpret the results of the air modeling estimates. Peak concentrations were compared to the 4-minute NOEL of 600 ppb and the LOEL of 1.9 ppm.

RESULTS

Two-hundred-fifty-two cases of irritant, non-specific systemic, and respiratory symptoms were associated with the metam-sodium application. These included 178 community residents or visitors and 74 employees of a carrot packing operation located in the affected neighborhood of Arvin. The most severe reported illness occurred in a community visitor with a history of pre-existing pulmonary disease, who was hospitalized for a week with respiratory distress. ISC3 Modeling indicated 1-hour MITC concentrations in the affected community ranged from 0.8-1.0 ppm, in the range of the LOEL, with peak concentrations between 2.4 and 3.2 ppm.

CONCLUSION

Estimated MITC concentrations during the episode exceeded both the 4-minute NOEL and 1-hourNOELby approximately four fold. The high concentrations of MITC present in the affected neighborhood may have been partially attributable to failure to immediately complete a required post-application water-treatment on 15 of the 100 treated acres. However, because of the limited area involved, the violation was unlikely to have accounted for the entire incident. Similar episodes may occur when metam-sodium fumigants are used adjacent to other rural communities.