Objective The objective of the study was to examine the effects of occupational exposure to diisononyl phthalate (DINP) on serum testosterone levels in male workers.

Methods From 2015 to 2018, 97 male workers were recruited from six French factories in the plastics industry. In a short longitudinal study, changes over 3 days in the level of total or free serum testosterone and DINP exposure were measured. DINP exposure was measured by urinary biomonitoring: mono-4-methyl-7-oxo-octyl phthalate (OXO-MINP), mono-4-methyl-7-hydroxy-octyl phthalate (OH-MINP) and mono-4-methyl-7-carboxyheptylphthalate (CX-MINP). We further analysed changes in follicle-stimulating hormone, luteinising hormone, total testosterone to oestradiol ratio and two bone turnover markers (procollagen-type-I-N propeptide, C terminal cross-linking telopeptide of type I collagen), and erectile dysfunction via standardised questionnaires (International Index of Erectile Function, Androgen Deficiency in Aging Males). Linear mixed models were used with the variables ‘age’ and ‘abdominal diameter’ included as confounder.

Results Increased urinary OXO-MINP was associated with a significant decrease in total serum testosterone concentrations, but only for workers who exhibited the smallest variations and lowest exposures (p=0.002). The same pattern was observed for CX-MINP but was not significant; no association with OH-MINP was detectable. More self-reported erectile problems were found in workers exposed directly to DINP at the workstation (p=0.01). No changes were observed for the other biological parameters.

Conclusions Short-term exposure to DINP is associated with a decrease in total serum testosterone levels in male workers. Our results suggest that DINP could present weak antiandrogenic properties in humans, but these need to be confirmed by other studies.