Effects Of Attapulgite On Cadmium Absorption And Relief On Biological Toxicity

Soil is closely related to the production and living of mankind, and as soil pollution problems caused by human activities become increasingly serious, heavy metal pollution of soil has currently become the hot spot issue of environmental management. According to the National Soil Pollution Status Investigation Communique, soil pollution is dominated by inorganic type, among which the exceeding rate of cadmium (Cd) point position is 7.0%, rendering extensive attention from the society at large being paid to cadmium pollution. Cadmium from the soil is likely to result in the in vivo broken cellular structure, suppressed photosynthesis, as well as reduced enzyme activity once it is absorbed by the crops whose yield and quality are seriously affected; what’s worse, it may ultimately endanger the human health through the enrichment of food chain.The major mechanism of cadmium adsorbed by attapulgite, which is the adsorbing material, under various initial concentrations, solid-to-liquid ratios, adsorption time, and pH values, and compares the adsorption effects of high-grade and low-grade attapulgite on cadmium through batch processing experimental method at the ion strength of 0.01 mol·L-1 NaNO3. Simultaneously, the article performs stabilization test on the cadmium-polluted soil, investigates the effects of a wide range of additive amounts of attapulgite on the biotoxicity of the polluted soil, and constructs the acute toxicity test and diagnostic method for cadmium-polluted soil so as to analyze the influence of attapulgite on the effectiveness of cadmium in the soil, and to probe the application feasibility of attapulgite in the actual repair engineering. The findings are as follows:1. The adsorption of Cd2+ on attapulgite was inversely proportional to the solid-liquid ratio,and proportional to the initial concentration of Cd2+ with the ionic strength being 0.01 mol·L-1. The sorption pattern of Cd2+ was consistent with Langmuir equation. The sorption of Cd2+on attapulgite was strongly dependent on pH.When the pH value was about 3,the highest adsorption capacity was attainted in 0.01mol·L-1 NaNO3 solution. The results indicated that Cd2+ reacted with attapulgite in aqueous solution as soon as they contacted,and a contact time of 3 h was enough to achieve sorption equilibrium.The absorption efficiency of attapulgite on Cd2+ in the solution is as follows:high-grade attapulgite> low-grade attapulgite.2.As the exposure time prolonged, the mortality of earthworms increased along with the enhancing cadmium concentration, with weight being remarkably inhibited in the treatment of 0% additive amount of attapulgite in the biotoxicity test, and at the 14th day of test, the medial lethal concentration of the controlled earthworms is LC50=527.12 mg·kg-1; while that in the treatment of 4.5% additive amount of attapulgite is LCso=1212.25 mg·kg-1. In the treatment of 9% additive amount of attapulgite, all earthworms survive. The test results indicate that, addition of attapulgite reduces the weight-inhibition rate. The proteins, SOD and CAT within earthworm have little response to cadmium, and their sensitivity is as follows: SOD>CAT-proteins. Within certain exposure time, the cadmium concentration of 576 mg·kg-1 may be the critical concentration that induces the maximum earthworm CAT activity in accordance with the exposure-dose effect relationship; besides, it is also the critical concentration at which proteins are induced, while that at which SOD is inhibited may be 360 mg·kg-1.3. Both the effective state content of Cd in the soil, together with the Cd content in the leaching agent are notably reduced when compare the soil treated with attapulgite addition and that without treatment 30 days after soil cultivation. While the effective state content of Cd in the soil and the Cd content in the leaching agent in soil treated with 4.5% and 9% attapulgite show no distinct changes 60 days after soil cultivation when compared with those 30 days after soil cultivation, indicating that the effective state content of Cd in the soil and the Cd content in the leaching agent generally reach stable equilibrium after 30 days of attapulgite acting on soil. Meanwhile, the Microtox biotoxicity test reveals that, addition of attapulgite can reduce the toxicity of the leaching agent when the Cd concentration in soil falls in the range of 225～576 mg·kg-1, which reduces the toxicity the leaching agent from moderate to low.