Application Of Bioluminescent Bacteria Bioassay On Determination The Toxicity Of Copper And Nickel In Chinese Soils

With the development of industrialization, urbanization, agriculture and breeding industry in our country, heavy metals into the fields from fertilizers, atmospheric deposition, sewage irrigation etc. result in the content of copper and nickel in soil exceeded environment standards and is harmful to ecological safety and human health. So it is necessary to monitor the soil metal contamination. Although chemical analysis can accurately determine total amount of heavy metals in soil, it is limited to evaluate the bioavailability (or toxicity) of heavy metals to organisms. Bioassay can give the direct information of biological effects of heavy metal in soils. Therefore, application the bioassay to study the bioavailability or toxicity of heavy metals in soil will provide scientific data for the ecological risk assessment of soil and soil environmental quality standards.Due to the soil animal bioassay (such as earthworm acute toxicity test) and plant bioassay (such as barley root elongation and tomato shoot growth) have disadvantages of long experimental period, it has some limitations on practical applications. Therefore, it is essential to set up rapid, sensitive, low-cost and easily operated bioassay to monitor the contamination and to assess the risk of metals in soils.As marine lux bacteria is limited to be used in soil samples, so the freshwater bioluminescent bacteria - Vibrio-qinghaiensis sp.-Q67 was applied to develop acute toxicity bioassay. This paper focus on the relationship between soil metal content and microbial toxicity, to investigate the soil factors controlling ecotoxicity of Cu and Ni added to soils, threshold values of soil Cu and Ni, to develop applicable, predictable, and empirical model in order to supply the scientific basis and methodology for establishing environment standards of Cu and Ni and environmental risk assessment in soils in China. The main results and conclusions are as follow:1. The factors affecting the application Vibrio-qinghaiensis Q67 in soil samples were investigated including the effect of pH and background solutions on the bioluminescence and metal toxicity of Q67 in order to determine the optimal conditions for freshwater luminescent bacteria Q67 applied in soil samples. The results showed that Q67 was suitable for the samples of pH 5.5 9.0 in soil environments. According to the bioluminescence and Cu toxicity measured using Q67 in different background solutions, it was found that the bioluminescence of Q67 was more stable in high level artificial soil solution than in other solutions, so that the high level artificial soil solution is suggested as the background solution for bioluminescent bacterial bioassay with Vibrio-qinghaiensis Q67.2. In the copper solutions, H⁺ (pH 5.0 6.5),Mg²⁺ and Na⁺ ions independently mitigate copper toxicity (Vibrio-qinghaiensis Q67). It decreased about 37- and 4-fold in the measured EC50 values corresponding to the increasing H⁺ activity from pH 6.5 to 5.0 and Mg²⁺ activity from 0 to 100 mM, respectively. Ca²⁺ (0 100 mM) and K+ (0 100 mM) had no significant influence on Cu toxicity. Using WHAM model to calculate the speciation of copper, the free Cu²⁺ can not alone to explain the Cu toxicity to Q67. 3. The toxicity thresholds measured by bioluminescent bacteria Q67 bioassay for Cu (or Ni) in 17 spiked Chinese soils were calculated based the measured added Cu (Ni) in soils. The Cu and Ni toxicity (EC50) varied from 71 to 1975 mg/kg and from 59 to 4219 mg/kg in soils, representing 28 and 71-fold variance, respectively. The variance of toxicity of Cu was less than Ni in 17 Chinese soils. It concluded that the soil properties affect copper toxicity more than nickel in 17 Chinese soils4. Simple and multiple linear regressions for 17 soils from bioluminescent bacteria Q67 bioassay between Cu (Ni) toxicity thresholds based on total metal concentrations and soil properties. Soil pH and soil CEC were the best soil properties to predict Cu and Ni toxicity from bioluminescent bioassay. The empirical models based on soil pH and CEC can predict well on toxicity thresholds by lux bacteria assay, it is important for environmental risk assessment and establishing environment standards of heavy metals in soils in China.