<p><i>Zuotai</i>, a known Tibetan medicinal mixture
containing insoluble cubic mercuric sulfide (β-HgS), has been used to treat
diseases with long history. The mercury leaching ratio from <i>Zuotai </i>in gastrointestinal pH environment
is one determinant factor for its bioavailability and biological effect.
However, the information is still scarce now. Therefore, the study was designed
to investigate the mercury leaching from <i>Zuotai</i>,
β-HgS, and α-HgS in different pH solutions</p><p>Solutions
with different pH values (1–13) were prepared from pure water, HCl solution,
and NaOH solution; the pH was monitored using a pH meter. The solutions were as
follows: HCl solution with pH = 1, HCl solution with pH = 3, HCl solution with
pH = 5, NaOH solution with pH =
7, NaOH solution with pH = 9, NaOH solution with pH = 11, and NaOH solution
with pH = 13. A solid-liquid ratio of 1:100 was adopted in all leaching
experiments. Digestion, peristalsis and emptying of drug in the
gastrointestinal tract were simulated <i>in
vitro</i>. We detected the mercury released in solutions using Automatic Direct
Mercury Analyzer. Leaching Ratio of Mercury (μg/g)=[Total Weight of Mercury
Released (μg)]/[Total Weight of Substance Tested (g)]</p><p>The results
showed that the mercury leaching
ratios of <i>Zuotai </i>at pH 1 and pH 13 were
significantly higher than those at each point within pH 3–11; the mercury leaching ratio of <i>Zuotai</i> at pH 1 was higher than that at pH 13. The mercury leaching ratio of β-HgS slightly decreased from pH 1 to pH 3
and significantly increased from pH 3 to pH 13. The mercury leaching ratio of
β-HgS at pH 13 was far higher than that at pH 1. For α-HgS,
the mercury leaching ratio also slightly decreased from pH 1 to pH 3 and then
gradually increased from pH 3 to pH 13. The mercury leaching ratio of α-HgS at
pH 1 was lower than that at pH 13.</p><p>
</p><p>Taken
together, strong acidic or strong alkaline environments would promote the
dissociation of mercury from <i>Zuotai</i>,
β-HgS, and α-HgS.</p
