Methyl isothiocyanate

Epidemiological data

Administrative data

Endpoint:

epidemiological data

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Dose-response assessment of airborne methyl isothiocyanate (MITC) following a metam sodium spill.

Author:

Alexeeff GV, Shusterman DJ, Howd RA, and Jackson RJ.

Year:

1994

Bibliographic source:

Risk analysis, 14(2):191-198

Reference 2

Reference Type:

publication

Title:

A community-based epidemiologic study of acute health effects from a metam-sodium spill on California's sacramento river.

Author:

Kreutzer RA, Hewitt DJ, Sun R, Draper W, Mangiamele D, Goldman L, Jackson R, Smith D, Shusterman D.

Year:

1996

Bibliographic source:

Toxicology and Industrial Health, 12(2):267-275.

Materials and methods

Study type:

cohort study (prospective)

Endpoint addressed:

acute toxicity: inhalation

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

no data

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Methyl isothiocyanate

EC Number:

209-132-5

EC Name:

Methyl isothiocyanate

Cas Number:

556-61-6

Molecular formula:

C2H3NS

IUPAC Name:

isothiocyanatomethane

Details on test material:

Vapam (metam sodium) decomposes to MITC and HS.

Method

Type of population:

general

Details on study design:

A tank car derailment in northern California in 1991 spilled metam sodium into Sacramento River, and released its breakdown product, MITC into the air. 705 individuals reported symptoms.

Exposure assessment:

estimated

Details on exposure:

TYPE OF EXPOSURE: Inhalation

TYPE OF EXPOSURE MEASUREMENT: Area air sampling
Air samples were collected in charcoal tubes by ARB and by TERRA, at numerous locations along the river, with sampling periods ranging from 1-24h. Measured MITC levels ranged from 0.2-37 ppb.

EXPOSURE LEVELS: MITC air concentration estimation = 2 methods (physiochemical properties, and Air-to-water ratio)
The estimated peak levels were consistent between the tho methods (340-1300 ppb vs 140-1600 ppb).

EXPOSURE PERIOD: 9 days after the spill.

POSTEXPOSURE PERIOD: 2 weeks atfer the spill.

DESCRIPTION / DELINEATION OF EXPOSURE GROUPS / CATEGORIES: no data

Statistical methods:

no data

Results and discussion

Results:

EXPOSURE
Data from the ARB indicated that air levels along the river on the fourth day (12-hr integrated samples) ranged from 0.0007-0.124 mg/m3 (0.2-37 ppb). The 12- to 24-hr average levels reported by ARB on the fifth through the tenth day ranged from below the detection limit to 0.0085 mg/m3 (<0.1-2.6 ppb). The highest reported levels of MITC in air occurred in the Dunsmuir area, 4 days after the spill. The levels reported were 0.41 and 0.39 mg/m3 (125 and 119 ppb), based on a 1-hr sample taken near the water/ air interface. Thus, they represent potential peak exposures, but not breathing level samples. Since air levels for the first 2 days after the spill were not available, potential air exposures were estimated. Using various estimates of volatization of MITC and dilution in air, the localized air concentrations of MITC may have risen to peak levels of 140-1600 ppb.

FINDINGS
Many individuals reported odors.

INCIDENCE / CASES
During in 2 weeks following the incident, over 240 individuals reported symptoms such as eye and throat irritation, dizziness, and shortness of breath. The first case came into the emergency room approximately 12hr after the spill and 27 cases were seen the day following the spill. Seven individuals required hospitalization (two patients had pre-existing asthma while another suffered from chronic obstructive lung disease).
Nausea, headache, and eye irritation were the most commonly reported symptoms during the first 5 days. In addition, throat irritation, dizziness, vomiting, and shortness of breath were frequentty reported by patients. Chest tightness, cough, abdominal pain, diarrhea, and skin rash were each reported by some patients. Some patients also exhibited hyperventilation or anxiety-like symptoms, including rapid breathing, tremulousness, and perioral and acrodigital paresthesias (tingling around the mouth and of the fingertips).
Epidemiologic curves demonstrated early exposures and symptom onset, with delayed visits to health care providers.
STATISTICAL RESULTS : no data

Confounding factors:

Persons aged 20-39 years had higher attack rates (18.9-21.5%) for irritation symptoms. Sex did not appear to be associated with visits to health care providers (12.4% males vs. 14.5% females). distance from the river appeared to only partially explain visits to providers for symptoms and thus was a poor proxy for exposure.

Strengths and weaknesses:

no data

Applicant's summary and conclusion

Conclusions:

The human symptoms reported were consistent with the irritative endpoints reported in laboratory animals following inhalation exposure to MITC. However, the gastrointestinal symptoms were unexpected due to the unsuitability of rodent models for this set of responses. Some individuals reported a tingling of the skin, which was not predicted from the animal studies, but has been reported among laboratory personnel exposed to vapor phase MITC. Dermatitis was also reported in some workers cleaning the Sacramento River after the spill, which is consistent with the cutaneous irritant effects of MITC. Unpredictability of reported symptoms may reflect differences in species sensitivity, human heterogeneity, or may have been secondary in nature, resulting from the stress and anxiety associated with the incident. Individuals with preexisting respiratory conditions are probably more sensitive to the acute respiratory effects of MITC.

Executive summary:

A tank car derailement in northern California in 1991 spilled metam sodium into sacramento River and released its breakdown product, MITC into the air. Over 240 individuals reported symptoms such as eye and throat irritation, dizziness, and shortness of breath. Measured MITC levels ranged from 0.2 -37 ppb and estimated peak levels ranged from 140 -1600 ppb.