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

We would like to comment on the interesting findings by Schenker et al. in the article "Pulmonary Function and Exercise-Associated Changes with Chronic Low-Level Paraquat Exposure" (1). First, we would like to emphasize the authors' conclusions that an association between long-term paraquat exposure with inefficient ventilation and oxygen desaturation during exercise suggests that paraquat may cause subclinical gas exchange abnormalities. The relationship between paraquat exposure and exercise-induced oxygen desaturation amongst Costa Rican banana, coffee, and palm oil farm workers is consistent with what we found amongst South African deciduous fruit farm workers (2). This is despite the fact that in the Costa Rican study the handlers had a substantially shorter work history (median = 8.5 compared with 16 years in the South African study) and also used protective equipment while in the South African study population they hardly do. The Costa Rican study also excluded participants greater than or equal to 40 years of age from the most sensitive outcome, exercise testing. Workers in this age range, as the authors acknowledge, are likely the most exposed and vulnerable group in their study. Additionally, participants from smaller farms were excluded due to logistical difficulties. Moreover, the authors do not indicate if their exposure index included weighting for exposure task. Nonetheless, these two independent studies, conducted in different study populations and in different crop sectors, both found similar results and give strong support to the idea that chronic long-term paraquat exposure results in subclinical respiratory impairment.

Second, we would like to comment on the authors' conclusion that overall their findings do not show clinical effects associated with long-term paraquat exposure. This conclusion is based on (1) the results of the less sensitive outcomes used in their study as we and others have also found (3–5), and (2) results of exercise outcomes from a sample that excluded the most exposed and vulnerable participants, as pointed out above. The reason why no clinical effects due to long-term paraquat exposure have so far been demonstrated could be because the time period required for subclinical effects to achieve clinical relevance exceeds the study window of studies conducted so far. In our study, we calculated that a clinically relevant oxygen desaturation of 5% will result from lifetime paraquat exposure.

Mohamed Aqiel Dalvie, Leslie London and Jonathan E. Myers

University of Cape Town, Cape Town, South Africa

FOOTNOTES

Conflict of Interest Statement: M.A.D. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; L.L. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; J.E.M. 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. 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]
3. 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]
4. Howard JK, Sabapathy NN, Whitehead PA. A study of the health of Malaysian plantation workers with particular reference to paraquat spraymen. Br J Ind Med 1981;38:110–116.[Medline]
5. 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]

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