The average person in Hong Kong consumes fish or shellfish four or more times a week averaging about 60 Kg of fish per year. Even though the mean
mercury level in store-bought Hong Kong fish was only 0.12 mg/kg, corroborating evidence is presented from numerous studies to support the view that
mercury bioaccumulates. By the time a typical Hong Kong male reaches 30 years of age he will have accumulated approximately 4 mg/kg
mercury in his hair. By age 60, his hair
mercury levels will have increased to about 7.5 mg/kg. Hair is a useful
indicator of
mercury exposure. In the U.S. over a million hair samples have been examined for
mercury (mean, 1.5 mg/kg). The mean hair
mercury concentration for over 200 Hong Kong residents was 3.3 mg/kg which is more than double the U.S. mean (well over one standard deviation above the U.S. mean). Two lines of evidence support the hypothesis that fish is the major source of methyl
mercury in the diet of Hong Kong residents. 1. Individuals consuming 4 or more meals of fish per week had a hair
mercury of 4.07 mg/kg dry weight of hair while those consuming fish less frequently had significantly lower levels (2.56 mg/kg). 2. Hong Kong residents that consume no fish had only 0.38 mg/kg hair
mercury. The World Health Organization has adopted the U.S. EPA levels for
mercury and recommends that food with
mercury concentrations of 0.5 mg/kg or more should not be sold for human consumption. Data presented in this paper are consistent with the notion that adoption of a 0.3 mg/kg
mercury guideline would benefit residents in countries where rates of fish consumption are significantly higher than in the U.S. Japan, for example, has already adopted a 0.3 mg/kg
mercury guideline. In Hong Kong there is a significant correlation (p < 0.05) between
male subfertility and the level of
mercury in the hair of males between the ages of 25 and 75. Our study of individuals who have been eating
mercury contaminated fish steadily for many years suggests that a daily
mercury intake of only 0.3 to 0.7 mg/kg
body weight may be sufficient to inhibit spermatogenesis in some Hong Kong males.
Male subfertility has been correlated with both elevated
mercury and the presence of various organochlorines in the diet. To determine whether fish sold in Hong Kong with elevated levels of
mercury also had elevated levels of organochlorines we analyzed fish for both
mercury and organochlorine content of their dorsal muscle tissue. Because analysis of fish tissue for
lipids and a wide range of organochlorines is both very time consuming and expensive, only 15 different species of fish were tested. Organochlorine concentrations were low and there was no correlation between
mercury and organochlorine in the 15 fish tested for both organochlorines and
mercury. As a result of these tests we concluded that
mercury could not be ruled out as the principal causal factor associated with the lack of fertility in Hong Kong males.