Use of an improved method for analysis of urinary aflatoxin M₁ in a survey of Mainland China and Taiwan

An improved monoclonal antibody immunoaffinity chromatography/high- pressure liquid chromatography/fluorescence detection method was developed to measure aflatoxin (AF) exposure by quantifying AFM, in human and rat urine samples. Analysis of different amounts of various AF metabolites showed that the immunoaffinity resin was highly selective for aflatoxin B₁ (AFB₁), AFB₂, and AFM₁. Recovery of added AFs increased with the amount of immunoaffinity resin and was virtually complete within the range of 0.01-10 ng of AFM₁ by using 7 ml of resin. The detection limit of this method is 0.5 pg/ml urine. Rats dosed with tritiated AFB₁ excreted in their urine tritiatod AFM₁, among other AF metabolites, as indicated by chemical derivative confirmation and cochromatography with authentic AFM₁ and agreement of radioactivity and fluorescence quantitation. A linear dose- response relationship was found over the range of 0.05-50 μg/kg of body weight/day. Two humans dosed with 1.0 μg of pure AFB₁ excreted 6-7% of the dose as urinary AFM₁ over 5-7 days. Pooled urine samples from 30 men from each of 69 rural counties in mainland China and 16 survey areas in Taiwan, with two villages per county or area, were analyzed with this improved method (170 villages total). The correlation coefficient of urinary excretion of AFM₁ compared between villages within all 85 survey areas was 0.50 (P ≤ 0.001). Sixty-five % of the samples contained detectable concentrations of AFM₁ with an average excretion of 3.1 ng/12 h. Assuming an excretion rate of 26%, this AFM'1 excretion corresponds to a very low average daily AF consumption of 0.1-0.3 μg/day (possible range, 0-11 μg/day). Patterns of urinary excretion of AFM₁ were similar in mainland China and Taiwan.