Compared to the well-studied major
natural estrogens [i.e., estrone
(E1), 17β-estradiol (E2), and estriol (E3)], little information
is currently available for far-less studied natural estrogens such
as 2-hydroxyestrone (2OHE1), 4-hydroxyestrone (4OHE1), 16α-hydroxyestrone
(16α-OHE1), 2-hydroxyestradiol (2OHE2), 4-hydroxyestradiol (4OHE2),
17-epiestriol (17epiE3), 16-epiestriol (16epiE3), and 16-ketoestradiol
(16ketoE2) in surface water. In this study, seven natural estrogens
(E1, 2OHE1, 16α-OHE1, E2, 4OHE1, 2OHE2, and 17epiE3) were found
in the water of the Pearl River, with detection frequencies of 96%,
80%, 60%, 40%, 28%, 12%, and 12%, respectively. The mean concentrations
of the detected natural estrogens decreased in the following order:
2OHE1 (12.0 ng/L) > 16α-OHE1 (8.3 ng/L) > E1 (5.2 ng/L)
> 4OHE1
(2.6 ng/L) > E2 (2.3 ng/L) > 2OHE2 (1.1 ng/L) > 17epiE3 (0.5
ng/L).
In addition, the estrogen equivalence (EEQ) contribution ratios of
the far-less studied natural estrogens ranged from 0% to 94%, of which
EEQ ratios of 37.5% of the sampling sites exceeded 50%. What’s
more, if only the three major natural estrogens are considered, the
number of sample sites at high risk will be reduced from 13 to 1.
This work clearly shows that the current water safety assessments,
which are only based on well-known major estrogens, need to be re-examined
and updated with care.