Abstract：It is of great significance to evaluate the soil pollution status of cultivated land using the indicators of available-state heavy metals to reflect the real pollution status of the soil. The heavy metals in soil should be leached before the determination of available state.When diethyltriamine pentaacetic acid (DTPA)-triethanolamine (TEA)-calcium chloride (CaCl2) composite leaching system was used to extract the available-state heavy metals in the soil, it was found that the blank value of available-state Zn was relatively high, which had a certain influence on the determination of Zn. According to the concentration of each component in DTPA-TEA-CaCl2 composite leaching system, the corresponding solution of single component (i.e., DTPA, TEA and CaCl2) was prepared for the determination of blank value of available-state Zn. It was found that more than 93% of blank value of available-state Zn was from CaCl2 in DTPA-TEA-CaCl2 composite leaching reagent. Therefore, it proposed to use Ca(NO3)2 to replace CaCl2 in DTPA-TEA-CaCl2 system for the extraction of available-state heavy metals. In other words, a new DTPA-TEA-Ca(NO3)2 system for the leaching of available-state heavy metals in soil was developed. Moreover, the leaching conditions were optimized. The results showed that the optimal conditions for DTPA-TEA-Ca(NO3)2 system were listed as follows: the pH of 0.005mol/L DTPA-0.1mol/L TEA-0.01mol/L Ca(NO3)2 solution was 7.2; the ratio of soil (mass of soil, g) to liquid (volume of leaching agent, mL) was 1∶4; the sample was leached on reciprocating oscillator with rate of 180 r/min at 20℃ for 2h. Eight available-state heavy metals in standard soil sample, including Cu, Pb, Zn, Ni, Cd, Cr, As and Hg, were leached with DTPA-TEA-Ca(NO3)2 system and DTPA-TEA-CaCl2 system, respectively. The measured results were compared. It indicated that the measurement results of available states of elements were consistent with the certified values for both methods. In other words, the leaching effect of eight available-state heavy metals by two systems was same. It was further found that the determination result of available state of Zn was more close to the certified value in DTPA-TEA-Ca(NO3)2 system. Moreover, the average value of blank was about 81.4% lower than that in DTPA-TEA-CaCl2 system, which further proved that the replacement of CaCl2 in DTPA-TEA-CaCl2 system by Ca(NO3)2 could effectively reduce the interference of blank value of Zn with the determination results.
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