Speciation Analysis And Environmental Effect Of Radioactive Element And Typical Heavy Metals In Paddy Soil Around Uanium Tailings

Radioactive elements and heavy metals had been diffusing into paddy soils around uranium tailings fields,for many years,under the action of rain wash,seepage,gravitational force,wind power,etc.These pollutants bioaccumulated in human body and aquatic animals by soil-rice-human ecological chain and it harmed to people.In this study,the paddy fields around uranium tailings in southern China within 2 km was selected as the study area.By means of large sample collection and laboratory analysis,the pollution characteristics parameters of radioactive elements and toxic heavy metals in paddy soil were studied in terms of total concentrations,chemical forms of radioactive elements in paddy soil.At the same time,the temporal and spatial distribution trends,environmental risks,and bioavailability were systematically studied.On this basis,the migration rules of radioactive elements and typical heavy metals in paddy soil-root-stem-rice system were analyzed,and the internal relations of compound pollution and the influencing factors were summarized.The main findings include:1)Based on the concentration of radioactive elements and toxic heavy metals in paddy soil,the soil environmental system was assessed by the contamination factor,the Nemero synthesis pollution index and the potential ecological risk index adding uranium element,and the time-space distribution trend was studied.The study showed that there was alarming pollution and high potential ecological risk in the first area(within 0–1 km of the tailing reservoir),which was caused by high levels of Cd,As,U,Cu and Hg.The pollution level of the second area(within 1–2 km)was relatively low and still had considerable potential ecological risk.Hg and As were determined as the main pollutants.The distribution trend of the temporal and spatial shows that the pollution degree is high in the range of 100-200 m from the uranium tailings,and then the farther away from the uranium tailings dam,the pollution degree decreased at first and then increased.Both at the lowest altitude and in the rage of 800-900 m from uranium tailings dam,the pollution degree was the most serious.The paddy field in the rage of 1-2 km far from uranium tailings was less affected by the activity of the uranium tailings because of there was a mountain barrier between them.The pollution levels of each element in paddy soil decreased with the passage of time,and the migration rate varied with the variety of elements.2)Method of modified Tessier and BCR procedure were used to extract the chemical forms of elements in paddy soil with different particle sizes,the extraction concentration of different elements depended upon different particle size.The extraction ratio of U,Cr,As,Cu,Zn and Hg was the same in two methods.Based upon precision and accuracy,BCR procedure was better than method of modified Tessier.3)The acid soluble,reducible,oxidizable,residual forms of radioactive elements and typical heavy metals in paddy soil downstream of uranium tailings dam were studied by BCR method.It was found that U,Pb,Cu,Zn were mainly in the acid soluble and residual forms,and the extraction ratio of the four forms of Cd,As,Hg was uniform,while Cr was mainly in the residual form.The farther away from the uranium tailings,the lower the concentration of U and Pb,the higher the concentration and total concentration of Cu,Zn in the first region and the lower in the second region.The content of extractable state of Cd was increased,the content of total and four forms of Hg was decreased,and the ratio of residual form of Cr was decreased.The bioavailability study showed that the content of each element in system of paddy soil-root-stem-rice were decreased gradually,while U and Pb enriched in root,and the enrichment ability of Cu,Zn in each stage was higher.Cd,As was enriched in the root and stem,and the enrichment ability of Hg,Cr to rice was low.Correlation analysis showed that there were many correlations between soil elements and elements,as well as between soil and plants.By considering the limiting value of radioactive elements and heavy metals in rice,the content of Cd,Cr in the two sites exceeded the limit value of food pollution stipulated by the state,which might cause harm to the edible population.In addition,the soil pH range of 4.18 ~ 5.34(control area 5.00)in the study area was generally acidic,which was beneficial to the transformation of elements residual form to non-residual forms.