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Respiratory Health Effects Due to Long-Term Low-Level Paraquat Exposure

The comments from Dr. Dalvie and his colleagues are gratefully appreciated. The study we conducted in Costa Rica attempted to improve on previous studies through better exposure characterization by using biological monitoring, conducting assessments on a larger sample size, and using more sensitive outcome measures.

We agree that these results apply to the population studied and one limitation of our study was the exclusion of participants greater than or equal to 40 years of age from exercise testing, likely to be the workers most exposed to paraquat (1). However, standard measures of respiratory function, spirometry and carbon monoxide diffusing capacity tests completed by the full study population failed to show an association with paraquat exposure. These results were also consistent with the absence of an association of paraquat exposure and O₂ peak measures on the subset of workers < 40 years of age obtained during maximal cardiopulmonary exercise tests (1). No previous studies have directly measured oxygen uptake during exercise. We are less convinced that the desaturation results obtained through pulse oximetry, which were statistically not significant in our study, are more clinically relevant and indicative of respiratory compromises due to paraquat exposure.

Comparisons of exposure across studies are difficult to interpret due to differences in crops, field application methods and methods used to assess exposure. None of the previous studies examining paraquat exposure and respiratory health in agricultural workers used identical methods for exposure characterization. We used direct biological measures of exposure, but other studies have relied on job classification or skin rash symptoms from direct exposure (2–4). Comparisons of paraquat exposure in different populations using the more sensitive biological markers developed in this project would address comparability of exposure (5).

Marc B. Schenker and Maria T. Stoecklin

University of California, Davis, California

FOOTNOTES

Conflict of Interest Statement: M.B.S. states that this research was funded by Syngenta Crop Protection AG "Study of Agricultural Lung Disease" from 1/1/01–6/30/04 and the total costs were $868,548; M.T.S. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Schenker MB, Stoecklin M, Lee K, Lupercio R, Zeballos RJ, Enright P, Hennessy T, Beckett LA. Pulmonary function and exercise-associated changes with chronic low-level paraquat exposure. Am J Respir Crit Care Med 2004;170:773–779.[Abstract/Free Full Text]
2. Castro-Gutierrez N, McConnell R, Andersson K, Pacheco-Anton F, Hogstedt C. Respiratory symptoms, spirometry and chronic occupational paraquat exposure. Scand J Work Environ Health 1997;23:421–427.[Medline]
3. Dalvie MA, White N, Raine R, Myers JE, London L, Thompson M, Christiani DC. Long-term respiratory health effects of the herbicide, paraquat, among workers in the Western Cape. Occup Environ Med 1999;56:391–396.[Abstract/Free Full Text]
4. Senanayake N, Gurunathan G, Hart TB, Amerasinghe P, Babapulle M, Ellapola SB, Udupihille M, Basanayake V. An epidemiological study of the health of Sri Lankan tea plantation workers associated with long term exposure to paraquat. Br J Ind Med 1993;50:257–263.[Medline]
5. Koivunen ME, Gee SJ, Park EK, Lee K, Schenker MB, Hammock BD. Application of an enzyme-linked immunosorbent assay for the analysis of paraquat in human-exposure samples. Arch Environ Contam Toxicol 2005;48:184–190.[Medline]

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