Abstract: Sulfur (S) plays a key role in Hg biogeochemical cycle. To understand the effect of S in different chemical forms (S, Na₂SO₄, Na₂S) on absorption of Hg in mangrove plants, a pot experiment was conducted with Bruguiera gymnorrhiza (L.) Lamk seedlings treated with different chemical forms of S (S, Na₂SO₄, Na₂S) at different concentrations (0, 0.1% S, 1% S). The potting soil was taken from a farmland with Hg pollution. Sulfur (S₀), sodium sulfate (Na₂SO₄), or sodium sulfide (Na₂S) was added in the soil. Contents of total mercury (THg), methylmercury (MeHg) and sulfur in different organs of B. gymnorrhiza were determined. The results showed that Hg absorption in stem increased under stress of the three different sulfur compounds, while the situation in root and leaf was more complicated and irregular. Sulfur’s chemical forms predominantly affected the MeHg content in the root, and sulfuradding enhanced MeHg concentration in root. There was a significant positive correlation among contents of sulfur, Hg, and MeHg in the roots (P<0.01). On the contrary, the correlation between sulfur content and mercury content in aerial parts of stems and leaves was not significant (P>0.05).

Key words: intensity of fertilization, proportion of NPK, environmental safety threshold, environmental risk assessment.