Effects of paraquat ban on herbicide poisoning-related mortality

Abstract

Introduction Paraquat is a life-threatening poison. In Korea, approval for the use of paraquat was discontinued in November 2011 and a complete sales ban took effect in November 2012. The suicide mortality by pesticide was decreased from 5.26 to 2.67 per 100,000 populations between 2011 and 2013. A single center study showed that the total number of suicide attempts decreased, and the proportion of paraquat to pesticides decreased from 63.4% to 24.5% from 2011 to 2014. The purpose of this study is to evaluate the effect of paraquat ban on incidence and mortality of herbicide poisoning in Korea.

Materials and Methods This retrospective study involved herbicide poisoning patients who were admitted to emergency medical facilities throughout South Korea between January 1, 2010 and December 31, 2014. To determine if there were any changes in the characteristics before and after the paraquat sales ban, an analysis was performed using a chi-square test and independent two sample t-test. P-value < 0.05 was considered statistically significant. We performed univariate analysis to evaluate relationships among demographic characteristics. And identified independent prognostic factors for death of herbicide intoxication using multivariate logistic regression analysis integrating major covariates (selected here as variables with a P <0.05) indicated from our univariate analysis. Results were expressed as odds ratios (ORs) and 95% confidential intervals (CIs). To determine if there were any changes in the mortality rates before and after the paraquat sales ban, and to determine the time point of any such significant changes in mortality, the R version 3.0.3 (package, bcp) was used to perform a Bayesian change point analysis

Results A total of 2,257 patients were selected as study subjects and consisted of higher number of males (n=2,053, 90.9%). There are significant difference between the survival group and the death group except sex. The univariate analysis revealed that age, herbicide type, exposure route, paraquat ban, sex, co-ingestion, dose and intention were significantly different between death and survival. The multivariate logistic regression model revealed that same result to univariate analysis except paraquat ban and exposure route. In the Bayesian change point analysis, major increase in the change rate of herbicide mortality was observed in February 2012 , approximately 3 months after the paraquat ban was enforced, which correlates with a prominent decrease in the mortality rate. After that, the mortality rate decreased slightly and then stabilized until November 2013, when it dropped by a wide margin. This resulted in another major increase in the change rate that was higher than the previous change. This was approximately 1 year after the complete sales ban in November 2012.

Conclusions This study suggests that the paraquat ban affected to decreased intentionality for herbicide ingestion and it is contributed to lowering the mortality rate associated with herbicide poisoning. The change point analysis shows that certain time frame may be required for the effects of the regulatory measures to manifest.