氢氧化铁和腐殖酸结合态镉在文蛤体内的富集

Bioaccumulation of cadmium bound to ferric hydroxide and humic acid by the bivalve Meretrix meretrix Linnaeus

氢氧化铁和腐殖酸是沉积物中重金属的重要储存库,在一定程度上均可以控制重金属在底栖生物体内的富集.本文在3个浓度梯度(70、140、280mg·kg-1)下,通过颗粒物悬浮系统,研究了氢氧化铁和腐殖酸颗粒上附着的Cd在文蛤体内富集规律.实验结果表明,氢氧化铁和腐殖酸结合态Cd对文蛤的生物有效性存在显著差异.在Cd浓度为70mg·kg-1和140mg·kg-1时,氢氧化铁结合态Cd在文蛤体内均没有明显的积累,而腐殖酸结合态Cd则从140mg·kg-1起即可以在文蛤体内富集.在同一Cd浓度下,腐殖酸结合态Cd的积累速率高于氢氧化铁结合态Cd,然而,当文蛤体内Cd浓度达到约～0.7μg.g-1鲜重时,腐殖酸结合态Cd在文蛤体内的富集会趋于"稳态",而氢氧化铁结合态Cd则仍处于线性吸收阶段.一般认为有机质结合态重金属与无机氧化物结合态重金属相比,其生物有效性较高,然而,本实验结果显示,在较高的污染物浓度下及长期暴露过程中,当体内重金属浓度达到一定水平时,结合在无机颗粒物上的重金属可能更容易在生物体内富集到比较高的水平.

Ferric hydroxide and humic acid are important pools of trace metals in sediments and largely control trace metal accumulation by benthic animals. In this work,we investigated bioaccumulation of cadmium adsorbed on ferric hydroxide and humic acid particulates by the bivalve Meretrix meretrix Linnaeus at Cd loading concentrations of 70,140 and 280 mg·kg^-1. The results showed that the bioaccumulation characteristics were distinctly different for the two types of substrates. Bioaccumulation from ferric hydroxide was not observed at 70 and 140 mg·kg^-1,while the clams started to absorb Cd at 140 mg·kg^-1 from humic acid and the bioaccumulation rate was faster than that from ferric hydroxide. Bioaccumulation of Cd from humic acid reached a plateau of-0.7 μg·g^-1 wet weight and remained constant at that level with increasing exposure time,however,no steady state was achieved for Cd-Fe（OH）3 systems. This suggests that bivalves may not necessarily accumulate more trace metal associated with organic matter,even though this speciation is considered more bioavailable than that associated with oxide minerals.