Background The widespread use of herbicides has led to environmental contamination and has implications for human health. The liver is an important organ for the detoxification of environmental pollutants; however, studies on the association between herbicide exposure and liver function are limited.

Objectives To investigate the association between baseline serum herbicide levels and changes in liver enzyme levels and liver enzyme abnormalities over a 5-year period in middle-aged and older adults.

Methods This study was based on a nested case-control population of type 2 diabetes established in the Dongfeng-Tongji cohort, with a total of 1388 subjects included in this study and followed up for 5 years. Epidemiological data were collected through questionnaires, and baseline serum concentrations of three herbicides (metolachlor, propham, and acetochlor) were measured by gas chromatography-triple quadrupole mass spectrometry. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were detected at baseline and follow-up visits. The associations between baseline serum herbicide levels and changes in AST and ALT over 5 years were assessed using linear regression models with herbicide levels categorized into quartiles, adjusting for age, sex, education level, smoking status, drinking status, physical activity, body mass index, and new-onset type 2 diabetes occurred during follow-up. The relationship between baseline serum herbicide levels and the risk of liver enzyme abnormalities during follow-up was further analyzed using logistic regression models.

Results The positive rates of metolachlor, propham, and acetochlor were all higher than 80%, and their spiked rates of recovery ranged from 73.46% to 106.77%. The mean ± standard deviation of the age of subjects at baseline was (62.7±7.6) years, with 34.1% being male. The median serum levels of metolachlor, propham, and acetochlor at baseline were 0.05, 0.16, and 0.03 ng·mL⁻¹, respectively. There was no significant difference in baseline serum herbicide levels between the normal and abnormal liver enzyme groups at follow-up (P >0.05). The baseline liver enzyme levels and the changes in AST and ALT over 5 years in those who developed abnormal liver enzymes were significantly higher than those in the normal liver enzyme group (P <0.05). The linear regression analysis showed that the changes in AST increased progressively over 5 years in the second, third, and fourth quartiles of propham compared to the lowest quartile group (the second quartile: b=1.49, 95%CI: 0.10, 2.87; the third quartile: b=1.52, 95%CI: 0.14, 2.90; the fourth quartile: b=1.69, 95%CI: 0.31, 3.08; P <0.05). The associations of serum metolachlor and acetochlor with changes in AST were not significant. Additionally, no significant relationships were found between the three serum herbicides and the changes in ALT over 5 years or the risk of liver enzyme abnormalities.

Conclusion Serum propham levels in middle-aged and older adults are positively associated with changes in liver enzyme AST, which may have an effect on liver function. More studies are needed to provide scientific evidence for the association between herbicide exposure and liver function.