Statistical Analysis of Long-term Health Effects of Thailand's Oil Spill on the Health of Spill Cleaners

Abstract

The Rayong oil spill was caused by a ruptured pipeline and leaked over 50,000 litres of crude oil into Thailand's Gulf. The clean-up activities included personnel from the PTT Global Chemical (PTTGC), the Thai Navy and civilian volunteers. Annual follow-up visits were conducted in which the oil spill clean-up workers visited the Rayong hospital for health assessment from 2014 to 2018. However, no longitudinal study has been conducted to evaluate the possible long-term adverse effects of the Rayong oil spill exposure on the workers who participated in the clean-up activities. This study aimed to investigate the long-term health effects of the Rayong oil spill on haematological, renal, and hepatic indices of the clean-up workers using the data from Rayong hospital's 5-year health follow-up protocol. Data for this study was obtained from the Rayong hospital and included the haematological, hepatic, and renal indices of 869 workers who participated in the oil spill clean-up and attended at least one follow-up visit between 2014 and 2018. Haemoglobin (HB), haematocrit (HCT), white blood cell (WBC) count, red blood cell (RBC) count, and platelet count for haematological function. Other haematological indices were mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), polymorphonuclear neutrophils (PMN), and Lymphocytes (LYM). Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were assessed for hepatic function, creatinine (Cr) and blood urea nitrogen (BUN) for renal function. An endpoint analysis was conducted using analysis of variance (ANOVA) to determine the annual changes of the haematological, hepatic, and renal indices between the baseline in 2013 and the final follow-up in 2018, using the level of exposure to differentiate between subjects. The generalised estimating equations (GEEs) were used to determine the longitudinal trends of the indices, while latent class trajectory analyses were used to assess the presence of latent clusters based on the longitudinal trends. The results showed increasing trends of WBC (0.02 ± 0.01 × 103 cells/μL per year), RBC count (0.008 ± 0.01 cells/μL per year), platelet count (3.44 ± 0.39 × 103/μL per year), BUN (0.22 ± 0.03 mg/dL per year) and CR (0.01 ± 0.00 mg/dL per year). On the other hand, the average trends of LYM (-0.14 ± 0. 07% per year) and AST (-1.63 ± 0.20 IU/L per year) were decreasing. The level of exposure showed no significant effects on the trends of all but one of the haematological, hepatic, and renal indices. Gender and occupation were significantly associated with HB, platelets, MCHC and BUN trends. Clean-up workers from the PTTGC (0.31 ± 0.10) and military personnel (0.42 ± 0.18) had significantly lower trends of HB than civilians. The HB trend among men was 1.94 ± 0.12 times higher than women. The findings from this study indicate significant differences between the levels of some haematological, hepatic, and renal indices at baseline and final follow-up. Long-term trends found in this study, coupled with the significant increasing latent trends of some clean-up workers, indicate worsening renal functions due to oil spill exposure. Furthermore, results from this study show the possibility of cardiovascular effects among some of the oil spill clean-up workers 5 years after the clean-up.