Cohort study of workers at a New Zealand agrochemical plant to assess the effect of dioxin exposure on mortality

Abstract

ObjectivesTo describe how the exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) influenced mortality in a cohort of workers who were exposed more recently, and at lower levels, than other cohorts of trichlorophenol process workers.DesignA cohort study.SettingAn agrochemical plant in New ZealandParticipants1,599 men and women working between 1 January 1969 and 1 November 1988 at a plant producing the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) with TCDD as a contaminant. Cumulative TCDD exposure was estimated for each individual in the study by a toxicokinetic model.Primary outcome measuresCalculation of cause-specific standardised mortality ratios (SMRs) and 95% confidence intervals (95% CI’s) compared those never and ever exposed to TCDD. Dose–response trends were assessed firstly through SMRs stratified in quartiles of cumulative TCCD exposure, and secondly with a proportional hazards model.ResultsThe model intercept of 5.1 ppt of TCDD was consistent with background TCDD concentrations in New Zealand among older members of the population. Exposed workers had non-significant increases in all-cancer deaths (SMR=1.08, 95% CI 0.86 to 1.34), non-Hodgkin lymphoma (SMR=1.57, 95% CI: 0.32 to 4.59), soft tissue sarcoma (one death) (SMR=2.38, 95% CI: 0.06 to 13.26), diabetes (SMR=1.27, 95% CI: 0.55 to 2.50) and ischaemic heart disease (SMR=1.21, 95% CI: 0.96 to 1.50). Lung cancer deaths (SMR=0.95, 95% CI: 0.56 to 1.53) were fewer than expected. Neither the stratified SMR nor the proportional hazard analysis showed a dose–response relationship.ConclusionThere was no evidence of an increase in risk for ‘all cancers’, any specific cancer and no systematic trend in cancer risk with TCDD exposure. This argues against the carcinogenicity of TCDD at lower levels of exposure.

Evaluation of genotoxicity after acute and chronic exposure to 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) in rodents using machine learning algorithms

“…Some studies have shown a small increase in the risk of cancer in workers exposed to herbicides contaminated with higher chlorinated dioxins (Kogevinas et al, 1997). However, other studies show that there is no increased risk for all types of cancer at lower levels of exposure to dioxins (McBride et al, 2018). In our study, the 2,4-D formulation is in accordance with the concentration of dioxins assessed as permissible by IARC (IARC, 2015).…”

Development of a Questionnaire for the Search for Occupational Causes in Patients with Non-Hodgkin Lymphoma: The RHELYPRO Study

“…The standardized NHL mortality ratio was 1.57 (95% CI: 0.32-4.59) in a New Zealand cohort of 1599 workers between 1969 and 1998 in a production factory of 2,4,5-trichlorophenoxyacetic acid contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The authors conclude that these results do not support the carcinogenicity of TCDD at low levels of exposure [23]. The recent meta-analysis of Satta et al did not show a relationship between exposure to ionizing radiation at dose levels generally encountered in the workplace and the occurrence of lymphomas [24].…”