Lindane use and the incidence of thyroid cancer in the United States; an ecological study

Abstract

Introduction: The increased thyroid cancer incidence rate may potentially be partially attributable to exposure to chemicals with endocrine disruptive properties. Lindane is an organochlorine pesticide with endocrine disruptive properties that has been classified as carcinogenic to humans. The aim of this ecological study was to evaluate potential correlation between Lindane exposure and thyroid cancer incidence in the United States (US). Methods: Data on age-adjusted thyroid cancer incidence rate (per 100,000 people) was obtained from the Centers for Disease Control and Prevention for all US states for 2018. Lindane use was obtained from the US Geological Survey and presented in quintiles for the years 1992 and 2007 to consider latency period. Trend of Lindane use between 1992 and 2007 was calculated using Mann Kendall correlation test. Lindane use estimates per cropland (kg/acres cropland) were overlaid on the map of age-adjusted thyroid cancer incidence rate using ArcGIS. Correlation between statewide Lindane use and age-adjusted thyroid cancer incidence rates was calculated using Spearman correlation. Results: Overall Lindane use decreased significantly between 1992 and 2007 (T= -0.617; p <0.001). Statewide differences in the patterns of Lindane use as well as thyroid cancer were found, with high rates of thyroid cancer and Lindane use reported in several states including Delaware and Georgia. There was no statistically significant correlation between thyroid cancer incidence rates in 2018 and Lindane use in 1992 (r=0.075; p=0.689) nor Lindane use in 2007 (r=0.01; p=0.935), among males and females combined. Conclusion: Restrictions clearly seem to be effective in reducing Lindane use. While, overall, there was no evidence of a correlation between thyroid cancer and Lindane use, more research is needed to explore this further specifically in highly exposed populations (e.g. rural areas) with longitudinal studies that assess the effects of long-term exposure to Lindane and other organochlorine pesticides.