Utility of Urinary 1-Naphthol and 2-Naphthol Levels to Assess Environmental Carbaryl and Naphthalene Exposure in an Epidemiology Study

P-150 Introduction: We recently reported associations between urinary 1-naphthol (1N) levels and several intermediate measures of male reproductive health, namely sperm motility, serum testosterone levels, and sperm DNA damage. However, because 1N is a major urinary metabolite of both naphthalene and the insecticide carbaryl, exposure misclassification stemming from differences in exposure source was probable and interpretation of the results was limited. Since naphthalene, but not carbaryl, is also metabolized to 2-naphthol (2N), the relationship of urinary 1N to 2N within an individual may give information about source of 1N. Methods: Utilizing newly available 2N data for each subject from our earlier reports, along with data from two previous studies that measured both 1N and 2N in urine of men exposed to either carbaryl or naphthalene, the present study employed several methods to differentiate urinary 1N arising from exposures to carbaryl and naphthalene among men in the reproductive health study. When reevaluating the reproductive health data, techniques for identifying 1N source involved exploring interaction terms, stratifying the dataset based on 1N/2N ratios, and performing an exposure calibration using a linear 1N to 2N relationship from a study of workers exposed to naphthalene in jet fuel. Results: Despite some inconsistencies in results between the methods used to distinguish 1N source, there was evidence that taking both 1N and 2N levels into account in our data served to reduce exposure measurement error. We found that 1N from carbaryl exposure is likely responsible for the previously observed association between 1N and sperm motility, while 1N from naphthalene exposure is likely accountable for the association between 1N and sperm DNA damage. Discussion and Conclusions: We recommend that studies of health effects associated with carbaryl utilize a 1N/2N ratio to identify subgroups in which 1N level is primarily from exposure to carbaryl. Conversely, studies of naphthalene-related outcomes may utilize 2N levels alone to estimate exposure.