Determination of aflatoxin M1 in urine samples indicates frequent dietary exposure to aflatoxin B1 in the Bangladeshi population

Aflatoxin B1 (AFB1), a hepatocarcinogen and highly toxic mycotoxin, is a contaminant of food commodities, especially in hot and humid climates that favour the growth of aflatoxin-producing fungi. As data on AFB1 contamination of food and feed in Bangladesh are scarce, we conducted an initial screening by ELISA on the occurrence of the metabolite and biomarker aflatoxin M1 (AFM1) in urines from Bangladesh which indicated frequent exposure. This finding led us to conduct a follow-up study where we applied a more sensitive method (IAC clean-up and HPLC-FD analysis) to determine AFM1 concentrations in a larger set of urine samples. To account for possible seasonal and regional differences in mycotoxin exposure, in total 218 urines were collected in two districts of Bangladesh: 164 urines (n = 69 in summer, n = 95 in winter) from residents of a rural and an urban area in Rajshahi district, among them 62 participants enrolled in both sampling periods, and 54 urine samples obtained from pregnant women in Dhaka district.AFM1 was detected in >40% of all Rajshahi urine samples at a range of 1.7-104 pg/mL in summer and at a range of 1.8-190 pg/mL in winter season. The mean level of urinary AFM1 was higher in winter (27.7 ± 42.6 pg/mL) than in summer (13.6 ± 21.2 pg/mL) season, and differences were observed at the mean AFM1 level between the rural and the urban Rajshahi cohort. AFM1 was found less frequently in the Dhaka pregnant women (31% above LOD, mean 13.9 ± 33.3 pg/mL), but in a similar concentration range (1.7-141 pg/mL) as in the Rajshahi cohort. Urinary AFM1 levels did not show significant associations with the participants food consumption pattern. In conclusion, when compared to biomarker data from other countries, detection frequency and urinary AFM1 levels in our Bangladeshi cohorts raise concerns regarding their exposure to potent carcinogenic aflatoxins.