Soil Heavy Metal Pollution
By identifying the distribution characteristics of heavy metal elements in Yuanmou County, we can understand the local heavy metal sources and environmental ratings, objectively grasp the environmental problems existing in the soil in this area, put forward scientific and reasonable suggestions for agricultural development and environmental governance, and improve the level of land management and environmental monitoring in this area. The method of combining traditional geochemistry and soil science was used, and the sampling was carried out according to the relevant standards of 1:250000 land quality geochemical survey. SPSS, Excel, GeolPAS.V4.5, ArcGIS10.8 and other software were used for data modeling, result integration and map production. The results showed that heavy metal elements As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were existed in the surface soil of Yuanmou County, in which Cd was enriched on the surface, and the anisotropy of Cd and Hg was higher than that of other elements. The overall distribution of Cu was balanced, with local characteristics of enrichment and depletion. Cr was highly correlated with Ni and weakly negatively correlated with Pb. There were three main sources of heavy metals: mainly rich in Zn and As, mainly rich in Cr, Ni and Cu, and mainly rich in Hg. In the comprehensive grade assessment of surface soil environment, the risk-free area was 1873 km2, accounting for 92.77%, and the risk-controlled area was 146 km2, accounting for 7.23%. The area was concentrated in Jiangyi Town, Guanyuan Town and Pingtian Town, and scattered in other areas, with no high risk area. The distribution of heavy metals As, Cr, Ni, Pb and Zn in Yuanmou County was mainly controlled by the parent material, Cu and Cd were controlled by the parent material, continuous weathering and human activities, and Hg was mainly controlled by human activities. There was no high-risk area in Environmental rating, and the risk controllable areas were mainly affected by Cu and Cd, among which the Cd risk controllable areas were highly consistent with the concentrated areas of agricultural development, and the application of relevant pesticides should be reasonably controlled and monitored in the later stage. Hg wasn’t at risk in the whole region, but there had been a slight enrichment trend in the surface soil, which required a late warning to avoid pollution.
Determining the safety threshold of heavy metals in soil is an important measure to ensure the quality and safety of agricultural products in China. By studying the accumulation and transportation characteristics of five heavy metals (Cr, Cd, Pb, As, and Hg) in different organs of corn and wheat in the cities of Jinchang, Zhangye and Baiyin in Gansu Province and establishing the relationship between the effective content of Cr, Cd, Pb, As, and Hg in soil and crop grains, this study identified the safety threshold of effective heavy metals in soil for corn and wheat systems. This study employed the method and principles of species sensitivity distribution (SSD) and derived the safety threshold of effective heavy metals in soil for corn and wheat planting systems based on the cumulative probability distribution curve of the Logistic function distribution model. The results showed that the accumulation pattern of Cr, Cd, Pb, As and Hg in wheat plants was consistent, namely, roots>stems>grains, and similarly, the accumulation pattern of Cr, Pb, As and Hg in corn plants was roots>stems>grains, while the accumulation pattern of Cd was stems>roots>grains. Utilizing the Logistic function distribution model to fit the cumulative probability distribution curve based on the effective content of heavy metals, the safety thresholds of effective Cr, Cd, Pb, As and Hg in wheat soil were determined to be 0.019, 0.771, 35.294, 2.777 and 0.133 mg/kg, respectively. Meanwhile, the safety thresholds of effective Cr, Cd, Pb, As and Hg in corn soil were determined to be 0.296, 7.90, 52.363, 12.462 and 0.119 mg/kg, respectively. The results of this study indicate that estimating the safe threshold of effective heavy metal content based on the cumulative probability distribution curve method was scientific, providing a scientific basis and support for the safe planting and risk control of wheat and corn.
In order to explore the pollution status and health risks of heavy metals in rice grains in a county of southern Henan, 68 rice grain samples were collected in the area in September 2021. The contents of chromium, arsenic, cadmium, lead, and mercury were determined by inductively coupled plasma mass spectrometry (ICP-MS-TQ) and direct mercury detection. The risk degree of heavy metals in rice was evaluated by single factor and Nemerowcomprehensive pollution index method, and the potential health risk of heavy metals from rice grains was evaluated by target hazard quotient (THQ) promoted by US EPA. The results showed that the average content of heavy metals in 68 rice grains did not exceed the Chinese Food Hygiene Standards, but the arsenic and cadmium contents in some samples exceeded the standards. The comprehensive pollution index (PN) of heavy metals in rice grain was 0.49, which was safe. ADD of adults and children was higher than RfD, and hazard quotients (HQ) of As were 3.11 and 4.80, which indicated that there was a certain risk of arsenic content in rice grains. The total hazard index (HI) of heavy metals to the exposed population was greater than 1, indicating that the long-term consumption of the rice by local residents may cause adverse health effects. In summary, the rice grain samples in the research area have been contaminated with arsenic, posing certain health risks. The local government needs to strengthen dynamic monitoring of the rice planting process, pay attention to the changes in the form and effective state of arsenic, ensuring food security.
To study the environmental pollution of paddy fields in a region of Sichuan, this paper focused on paddy soil and rice as the main research objects. A total of 216 soil and rice samples were collected from the area, and the heavy metal pollutants in soil and rice in the study area were evaluated by testing the content of eight heavy metal elements, namely arsenic, lead, cadmium, chromium, mercury, copper, zinc and nickel in soil, and the content of five heavy metals, namely arsenic, lead, cadmium, chromium, and mercury in rice, using the single-factor pollutant index method and the Nemero composite pollutant index method, as well as performing the quantitative analysis of the association between various heavy metal elements in soil and rice. The results showed that: (1) the average content of cadmium and mercury in the soil of this study area was 0.47 and 0.98 mg/kg, respectively, which exceeded the standard, and their exceedance rates were 27.78% and 34.26%, respectively. The combined pollution index of Nemero in this study area was 1.11 mg/kg and the pollution level was mild. (2) There were significant correlations between the eight elements in the soil and the pathways of heavy metal accumulation might be the same. The coefficient of variation of soil Hg was 163.20%, which was highly variable, indicating that local pollution sources had a strong influence on heavy metals in soil, and the exceeding of Hg content in soil was mainly anthropogenic. (3) Cadmium, chromium and lead in rice had exceeded the standards, with exceedance rates of 19.44%, 3.70% and 19.44%, respectively. The study shows that the degree of heavy metal enrichment in rice has some correlation with soil heavy metal content and is related to the chemical form of heavy metals. It has certain guiding significance for food safety and heavy metal pollution remediation and treatment.
To accurately assess the levels of heavy metal pollution, health risks and pollution sources in the surface soil of orchards in Qingyang City, the research team collected 16 surface soil samples at 0-40 cm soil layer from orchards in Qingyang City. The concentrations of chromium (Cr), cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), arsenic (As) and mercury (Hg) were determined. Based on the single factor pollution index, the Nemerow comprehensive pollution index, geo-accumulation index, potential ecological risk index and health risk appraisal model were used to evaluate the degree of heavy metal pollution and health risks. In addition, principal component analysis was applied to analyze the sources of heavy metal pollution. The results indicated that the soil of orchards in Qingyang City was severely polluted by cadmium (Cd), reaching a moderate pollution level. The geo-accumulation index for mercury (Hg) was greater than 5, indicating extreme pollution, while the geo-accumulation indices for other heavy metals were all below 0, indicating no pollution. The potential ecological risk index (RI) for the seven elements ranged from 1694.28 to 5158.06, indicating extreme pollution. The total non-carcinogenic risks for young adults (aged from 18 to 40) and middle-aged adults (aged from 41 to 60) were 0.12 and 0.09, respectively, indicating no non-carcinogenic risk to local orchard farmers from soil heavy metals. However, the total carcinogenic risks for young adults and middle-aged adults were 9.21×10-5 and 7.45×10-4, respectively, exceeding the acceptable level (1×10-6), indicating a carcinogenic risk from soil heavy metals to local orchard farmers. Source analysis suggested that the main sources of soil heavy metal pollution may be a combination of traffic and plastic mulch, pesticides, fertilizers, and atmospheric deposition.
To study the effect of the application of soil amendment on the Cd availability in soil and the Cd content in brown rice, a continuous three-year field experiment was conducted in two different textures of Cd contaminated paddy soil in Xiaojia Town, Hengyang City, Hunan Province. The results indicated that: (1) continuous application of soil amendment (2250 kg/hm2 and 3000 kg/hm2) for three years significantly increased the paddy soil pH in Jinxing Village and Niuling Village, and reduced the content of available Cd in soil by 14.1%-50.0% and 16.9%-49.4%, respectively; (2) continuous application of soil amendment for three years significantly increased the rice yield in Jinxing Village and Niuling Village, and reduced the Cd content in brown rice by 40.4%-62.9% and 40.0%-64.1%, respectively. Moreover, the Cd content in brown rice in both areas was 0.15-0.18 mg/kg under the treatment of applying 3000 kg/hm2 amendment, lower than the National Standards for Food Safety (GB2762—2022); (3) the net income of farmers in both areas increased significantly by 1603-2912 and 2282-3408 yuan/hm2, respectively, under the treatment of applying 3000 kg/hm2 amendment. Therefore, the application of soil amendment was a remediation technology that can achieve safe production in mildly Cd contaminated paddy soil.
This study briefly describes the impact of pollution by five heavy metal elements, namely cadmium, chromium, arsenic, vanadium, and copper, on the growth and quality of Lycium barbarum and other crops. It summarizes the mechanisms of L. barbarum to cope with the stress of cadmium, chromium, arsenic, and other five heavy metals, as well as the research progress on detoxification of heavy metal stress at the subcellular level in L. barbarum. The study points out the existing problems in current research on L. barbarum response to heavy metal stress and future research directions, such as the migration and transformation of heavy metal content between soil and various parts of the L. barbarum, including roots, stems, branches, leaves, and fruits, the response mechanisms of L. barbarum to heavy metal stress, and molecular mechanisms, in order to provide references for the application and improvement of clean cultivation of L. barbarum.
To investigate the efficiency of Sedum alfredii in extracting heavy metals from farmland under intercropping systems, this study employed the technique of intercropping the Cd-hyperaccumulator Sedum alfredii with sweet corn to conduct experiments in moderately cadmium-contaminated farmland in South China. The results indicated that under the intercropping system, the yield of sweet corn increased, and the Cd content in the kernels significantly decreased by 8.3% compared to monoculture. Additionally, under the intercropping system, the biomass of Sedum alfredii increased by 16.5%, with Cd accumulation in the roots and shoots increasing by 8.8% and 3.6%, respectively. The enrichment coefficients improved by 15.7 and 6.6 units, respectively. After intercropping sweet corn with Sedum alfredii, the Cd content in the top soil significantly decreased. The experiment demonstrated that the phytoremediation model of intercropping Sedum alfredii with sweet corn not only allowed for the simultaneous remediation and production of polluted farmland but also enhanced the extraction efficiency of the hyperaccumulator plant. This approach presented a practical and green remediation technology for moderately heavy metal-contaminated farmland.
Winter wheat is one of the main food crops in China. The enrichment characteristics and potential risks of heavy metals were discussed to provide reference for rational planting of wheat and grain safety and quality. The contents of Fe, Mn, Cu, Zn, Cr, Ni in soil and wheat grain samples collected from typical farmland in northern Henan were determined, and the pollution and ecological risk of heavy metals were evaluated. The results showed that the average contents of Fe, Mn, Cu, Zn, Cr, Ni in soil were 11397.33, 287.83, 23.33, 7.41, 31.41 and 8.56 mg/kg, respectively. Most of the elements showed a significant positive correlation; the single pollution evaluation and comprehensive pollution evaluation of Cu, Zn, Cr, Ni were clean. The average contents of Fe, Mn, Zn, Cu, Cr, Ni in wheat grains were 30.42, 61.75, 23.17, 1.52, 0.28 and 0.16 mg/kg, respectively. There was a significant positive correlation between individual elements. The contents of Fe, Zn, Cu were lower than the maximum tolerable content of wheat, and the content of Mn was higher than the maximum tolerable content of wheat. The comprehensive pollution evaluation of Cr was mild pollution, and the pollution evaluation of Ni was clean. There was a synergistic or antagonistic effect between heavy metals in the soil-wheat system. The enrichment coefficient of wheat grain to soil heavy metals was Zn > Mn > Cu > Ni > Cr > Fe. The risk of heavy metal pollution in farmland soil in northern Henan is low.
To evaluate the reduction effects of combined application of different nitrogen, phosphorus fertilizers and biochar on cadmium (Cd) availability and crop growth in Cd contaminated farmland soils, so as to provide scientific basis for the safe utilization of Cd contaminated farmland and the rational selection of nitrogen and phosphorus fertilizers. A pakchoi (Brassica chinensis L.) pot experiment was conducted to study the effects of combined application of three nitrogen fertilizers such as ammonium sulfate (L), urea (N), and calcium nitrate (X), two phosphorus fertilizers such as superphosphate (S) and calcium magnesium phosphate (C), and biochar (B) on soil Cd availability, pakchoi growth and Cd uptake from a farmland soil contaminated by Cd. The results showed that compared with the control treatment without fertilizer application, combined application of nitrogen and phosphorus fertilizers significantly increased the biomass of pakchoi by 28.6%-65.7%, and the combined application of nitrogen, phosphorus fertilizers and biochar significantly increased pakchoi biomass by 11.9%-40.0% compared to the treatment of combined application of nitrogen and phosphorus fertilizers. The combined application of calcium nitrate and calcium superphosphate significantly increased soil pH by 0.23 units, whereas other nitrogen and phosphorus fertilizer treatments had no significant impact on soil pH. However, content of soil available Cd in the treatments of combined application of all nitrogen and phosphorus fertilizers was decreased by 16.5%-38.8%, content of Cd in pakchoi was reduced by 5.87%-25.0%, compared with the control treatment. Compared with the combined application of nitrogen and phosphorus fertilizers, the combined application of nitrogen, phosphorus fertilizers and biochar increased soil pH in varying degrees with a maximum increase of 0.42 units, decreased the content of soil available Cd by 5.31%-56.3%, and decreased the content of Cd in pakchoi by 25.5%-4.8%. The results confirmed that reasonable selection and application of nitrogen and phosphorus fertilizers are crucial during the process of safe utilization of farmland contaminated by Cd, which can not only achieve the best economic benefits, but also generate positive environmental effects. Meanwhile, the application of biochar further enhances the passivation effect of nitrogen and phosphorus fertilizers on Cd activity in the contaminated soil.
Water management and arbuscular mycorrhizal fungi (AMF) are the key factors affecting cadmium uptake, distribution and antioxidant defense system in rice roots. It is important to explore the relationship and mechanism of the three factors to guide the safe production of rice fields. In this study, with rice ‘Hemeizan No.2’ and AMF Rhizophagus irregularis as experimental materials, under different water management conditions, the effects of AMF on cadmium uptake, distribution and effects of root antioxidant defense system in rice were studied under different cadmium pollution concentrations (0.2, 1.0, 5.0 mg/kg). The results showed that under the condition of non-mycorrhizal treatment, the cadmium content of rice under different water management conditions increased with the increase of soil cadmium content. Especially compared with long-term flooding, dry and wet alternations significantly increased the effective cadmium concentration in soil, promoted cadmium uptake in rice roots and increased cadmium content in straw. However, under different water management conditions, the addition of AMF increased the pH of different cadmium-contaminated soils, reduced the availability of soil cadmium, inhibited the transfer of cadmium from rice roots to the above-ground part, and thus reduced the cadmium content of straw and the enrichment effect of rice on cadmium. Especially under the condition of moderate cadmium pollution, the addition of AMF increased the activities of peroxidase (POD) and superoxide dismutase (SOD) in rice roots, and reduced the absorption of cadmium in rice roots (alternating dry and wet) and the distribution of cadmium in rice root subcells. Therefore, the addition of AMF can effectively reduce the accumulation of cadmium in the above-ground part of rice under the water management conditions such as long-term flooding and alternating of wetting and drying.
In order to reduce the harm of high lead-contaminated soil to crops, three additives of superphosphate, organic fertilizer and phosphorus rock powder were used to explore the remediation effect on high lead- contaminated soil in Guangxi through pot experiments. The results showed that compared with the control group T0, the application of superphosphate, organic fertilizer and phosphorus rock powder significantly reduced the harm of lead poisoning (P < 0.05) to different degrees, reduced soil pH and soil DTPA-Pb, water soluble Pb content, improved the survival rate and biological yield of pakchoi, and reduced the enrichment coefficient of lead in pakchoi. The above amendments can be used as the preferred improvement materials for high lead-contaminated soil in Guangxi.
Cadmium (Cd) pollution in farmland soil seriously affects the quality of cultivated land and food security. To provide new materials for the remediation of Cd pollution in farmland soil, the effects of co-pyrolysis biochar on Cd absorption and accumulation in rice and soil improvement were investigated by preparation and application of co-pyrolysis biochar. Field experiments were conducted to investigate the effects of three different amounts of peanut shell-corn straw co-pyrolysis biochar on Cd transport and migration characteristics and bioavailability in various organs of rice. The results showed that the application of co-pyrolysis biochar could reduce the accumulation of Cd in rice grains, reduce the toxicity to rice plants, increase soil fertility and promote the growth of rice. Compared with no co-pyrolysis biochar addition, the soil pH of biochar treatment increased by 0.06-0.12 units, and the contents of alkali-hydrolyzable nitrogen, available phosphorus and available potassium increased by 37.20%-78.27%, 49.62%-134.10% and 20.79%-35.26%, respectively. After adding co-pyrolysis biochar, the available Cd content in soil decreased significantly by 11.11%-26.98% (P<0.05), and the Cd content in rice grain decreased significantly by 23.46%-47.49% (P<0.05). The application of peanut shell-corn straw co-pyrolysis biochar in the field can improve soil fertility, soil environmental quality, and reduce Cd content in rice grains. The effect was most significantly when the amount of peanut shell-corn straw co-pyrolysis biochar was 15 t/hm2.
To assess the efficacy of five conditioning agents of lime powder (SCⅠ), dolomite powder (SCⅡ), oyster shell powder (SCⅢ), peat soil (SCⅣ) and silicate-calcium-magnesium-potassium fertilizer (SCⅤ) on passivation repair cadmium (Cd) pollution in paddy soils, this study conducted pot experiments using slightly acidic paddy soil with Cd pollution, and the effects of these conditioners on soil pH, the distribution characteristics of Cd speciation in the soil, and its bioavailability were monitored and analyzed. The results showed that after 60 days of each treatment, the soil pH increased by 1.81, 1.49, 1.17, 0.48 and 0.60 units, respectively. The distribution characteristics of water-soluble fraction, mild acido-soluble fraction, reducible fraction, oxidizable fraction and residue fraction Cd in the soil had changed in different degrees. Specifically, the distribution coefficient of water-soluble fraction Cd was reduced by 0.70%, 0.54%, 0.63%, 0.21%, and 0.24%, respectively; mild acido-soluble fraction Cd was reduced by 17.68%, 8.39%, 11.52%, 18.13%, and 15.95%; and the distribution coefficient of residual fraction Cd was increased by 14.27%, 5.33%, 11.54%, 17.70%, and 14.34% (P<0.05). This indicated that SCⅠ, SCⅡ, SCⅢ, SCⅣ and SCⅤ reduced the bioavailable Cd and increased the non-bioavailable Cd in the soil to varying degrees (P<0.05), and the passivation effects were 38.98%, 18.42%, 25.33%, 39.98% and 35.12% for Cd pollution in soils respectively. Therefore, all five conditioners demonstrated certain effectiveness in passivation repair Cd pollution in acidic paddy soils, warranting further test and verification demonstration application in safe utilization production technologies of Cd polluted acid paddy fields.
There is an urgent need for cadmium pollution transfer risk and soil nutrient restoration technology in rice field in karst mining area of South China. To explore the effect of nutritional passivator on cadmium (Cd) contaminated paddy soil in mining areas, and to clarify its effect on the morphological transformation, bioavailability and soil quality of cadmium in the rhizosphere soil of rice, the in-situ remediation experiment of paddy soil was carried out. Three treatments were set up, including no passivator (T1), inorganic nutritional passivator (T2) and organic-inorganic nutritional passivator (T3). The gradient diffusion film (DGT) technique was used to study the bioavailability of Cd and Cd transformation in rhizosphere soil of the paddy field, and the biological correlation between Cd transformation, bioavailability of Cd and soil quality was evaluated in rhizosphere soil of the paddy field. The results showed that: (1) nutritional passivator affected the ratio of cadmium formation in cadmium-contaminated paddy soil. Nutritional passivator could promote the transformation of exchangeable cadmium to residual cadmium in soil. Nutritional passivator reduced the proportion of exchangeable cadmium content. Compared with T1 (control), the T2 and T3 decreased the proportion of exchangeable cadmium content in soil by 14.71% and 5.88%, respectively. Nutritional passivator increased the proportion of reducible cadmium content. Compared with T1 (control), the T2 and T3 increased the proportion of reducible cadmium content in soil by 8.51% and 6.38%, respectively. Nutritional passivator increased the proportion of residual cadmium content. Compared with T1 (control), the T2 increased the proportion of residual cadmium content in soil by 10%, T3 had no obvious changes. (2) The bioavailability of Cd in rhizosphere soil of Cd-polluted paddy fields was reduced by treatment with nutritional passivator. Compared with T1 (control), the T2 and T3 treatments decreased bioavailability significantly by 54.21% and 50.47% at harvest stages. (3) Nutritional passivator improved soil quality in soil of Cd-polluted paddy fields. Compared with T1 (control), the T2 and T3 increased soil organic matter, pH and cation exchange capacity by 7.37%, 7.50% and 5.29%, 17.06% and 12.24%, 11.10%, respectively. Nutritional passivator could restore polluted soil and improve soil quality synchronously.
This study aims to explore the impact of the “VIP+n” comprehensive cadmium control technology system on cadmium-polluted paddy fields in the central and southern parts of Hunan Province. The experiments were conducted in Yaotian town of Leiyang City for two consecutive years, including plot comparative experiments and large-scale demonstration experiments. In the plot comparative experiments, 10 treatments were employed to compare the effects of measures such as low-cadmium-accumulating rice varieties, continuous flooding irrigation, application of quicklime, microbial agents, and foliar inhibitors on cadmium-polluted paddy fields. Based on the results of the plot experiments, three cadmium-reducing technologies with good efficacy and economic feasibility were selected for large-scale demonstration experiments. The results showed that the “VIP+n” cadmium control technology system effectively reduced the cadmium content in rice grains in cadmium-contaminated paddy fields. Compared to the control group, the cadmium reduction rate for early rice using this technology system ranged from 59.66% to 79.45%, while for late rice, it ranged from 46.85% to 48.23%. Among the various cadmium reduction measures, the application of quicklime significantly reduced the cadmium content in rice grains, and the use of low-cadmium varieties alone had a significantly higher cadmium reduction effect than using quicklime alone. In contrast, continuous flooding irrigation, application of microbial agents, and foliar inhibitors did not show significant cadmium reduction effects.
A soil incubation experiment was conducted to study the effects of cement, Mn-P modified biochar and Mn-P modified rice husk ash on soil pH and the available concentration of Cd, Pb and trace elements (Zn, Fe and Mn) in lead smelting site soils under four application rates of 0%, 1%, 2% and 4%. The results showed that with the increase of cement application rate, the pH of the lead smelting site soils significantly increased, and the availability of Cd and Pb decreased gradually. The soil pH of a smelting site in Jiyuan and a smelting site in Zhuzhou treated with cement increased by 0.89-1.84 and 0.89-1.76 units, respectively. The DTPA-Cd concentration treated with cement decreased by 34.3%-53.1% (P<0.05) and 59.6%-73.2% (P<0.05), and DTPA-Pb concentration decreased by 21.6%-44.7% (P<0.05) and 38.4%-44.3% (P<0.05), respectively. With the increase of application rates of Mn-P modified biochar and Mn-P modified rice husk ash, the soil pH, and Cd and Pb availability in lead smelting sites gradually decreased. The treatment of 4%Mn-P modified biochar reduced the soil pH of two lead smelting sites by 0.51 (Jiyuan) and 0.40 (Zhuzhou) units, respectively. The DTPA-Cd concentration significantly decreased by 18.0% (Jiyuan) and 39.8% (Zhuzhou), and DTPA-Pb concentration significantly decreased by 37.8% (Jiyuan) and 63.1% (Zhuzhou). The soil pH value of the two lead smelting sites treated with 4% Mn-P modified rice husk ash decreased by 0.70 (Jiyuan) and 0.23 (Zhuzhou) units, respectively. The DTPA-Cd concentration significantly decreased by 14.9% (Jiyuan) and 30.2% (Zhuzhou), and the DTPA-Pb concentration significantly decreased by 37.3% (Jiyuan) and 54.1% (Zhuzhou). The DTPA-Zn concentration in the soil of two lead smelting sites treated with 4% cement significantly decreased by 36.5% (Jiyuan) and 59.4% (Zhuzhou), respectively, and the DTPA-Fe concentration significantly increased by 122.7% (Jiyuan) and 142.9% (Zhuzhou), and the DTPA-Mn concentration significantly decreased by 13.8% (Jiyuan) and 69.1% (Zhuzhou), respectively. The treatment of 4% Mn-P modified biochar significantly increased the soil DTPA-Zn concentration by 48.7% (Jiyuan), and the DTPA-Mn concentration significantly increased by 409.7% (Jiyuan) and 538.6% (Zhuzhou), and the DTPA-Fe concentration significantly decreased by 33.4% (Jiyuan) and 30.7% (Zhuzhou), respectively. The treatment of 4% Mn-P modified rice husk ash significantly increased the soil DTPA-Zn concentration by 63.0% (Jiyuan), and the DTPA-Mn concentration significantly increased by 290.3% (Jiyuan) and 73.5% (Zhuzhou), and the DTPA-Fe concentration significantly decreased by 9.5% (Jiyuan) and 12.0% (Zhuzhou), respectively. The order of reducing Cd availability of three passivation materials in two lead smelting sites was cement>Mn-P modified biochar>Mn-P modified rice husk ash, and the order of reducing Pb availability was cement>Mn-P modified biochar>Mn-P modified rice husk ash (Jiyuan) and Mn-P modified biochar>Mn-P modified rice husk ash>cement (Zhuzhou). It was necessary to select suitable passivation materials based on the Cd and Pb pollution characteristics of lead smelting sites to achieve synchronous immobilization of soil Cd and Pb.
To explore the suitable passivation materials for ameliorating the farmland polluted by both cadmium and arsenic, pot experiments were carried out to compare the effects of five passivation materials on the reduction of cadmium and arsenic in rice grain. The materials included red mud, red mud + iron powder, basalt red mud + limestone powder, limestone powder + iron powder and limestone powder + biochar + ferrous sulfate. The experimental results showed that all of the five passivation materials could change the chemical forms of Cd and As in the soil, and reduce the bioavailability of Cd and As in the soil and contents of Cd and As in rice grain. On the whole, three kinds of compound passivation materials, red mud + iron powder, limestone powder + iron powder and limestone powder + biochar + ferrous sulfate, had the most obvious effect, which could reduce Cd and As in the grain by 58%-63% and 56%-67%, respectively. Under the experimental conditions, the five passivation materials did not lead to a significant decline in soil quality. The application of the passivation materials containing limestone powder and biochar was also conducive to reducing soil acidity, increasing soil organic matter and cation exchange capacity. Based on the comprehensive effect, red mud + iron powder is considered as an ideal passivation material for the treatment of Cd and As compound pollution of farmland soils.
Taking the farmland area of Dongyang as the research object, the safety of agricultural products was investigated mainly in the basic farmland protection area and the abnormal heavy metal area of soil geochemical investigation. The contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in the soil and crops of Dongyang were determined by point-to-point collaborative sampling method. Soil heavy metal pollution was evaluated by soil accumulation index and potential ecological risk index. The results showed that Cd and Pb pollution existed in the study area, compared with the risk screening value of agricultural land, the over-standard rates were 11.67% and 5.0%. There were Cd and As pollution in crops, compared with the limit of food pollutants, the content of heavy metals As and Cd in 70 pieces of rice samples exceeded the standard, and the over-standard rates were 25.71% and 10.0%; The heavy metal Cd in 14 pieces of taro samples exceeded the standard, and the over-standard rate was 42.86%. Soil pollution evaluation showed that heavy metals such as Cd had strong ecological risk, while other heavy metals had slight ecological risk acceptable range. Correlation analysis showed that As and Cr in soil had antagonistic effects on the absorption of rice, while Cu and Ni in soil had promoting effects on the absorption of Cd in rice. As and Ni in soil had antagonistic effects on the absorption of Cu, Cr, Pb and Zn in taro, while As and Ni in soil had promoting effects on the absorption of Cd in taro.
To explore the effects of different passivation materials with foliar inhibitor technology on the remediation of cadmium polluted farmland, screening the targeted remediation materials, this study selected a typical moderate and mild cadmium polluted farmland for demonstration, and adopted two different passivation materials with foliar inhibitor technology to study the effects on soil pH, available Cd and Cd content in various parts of rice. The results showed that compared with the control (CK), the pH of different treatments all increased to a certain extent (0.5%-12.5%). In SF1 and SF2, the available Cd content decreased by 23.4%-36.7% and 15.1%-30.8%, respectively; the Cd content in rice roots decreased by 70.5%-79.4% and 65.2%-72.6%, respectively; the Cd content in stems and leaves decreased by 36.7%-50.0% and 18.8%-38.4%, respectively; the Cd content in brown rice decreased by 60.1%-74.4% and 47.4%-72.2%, respectively; it could be seen that both passivation materials could effectively reduce the content of available Cd in soil, affected the enrichment of Cd in various parts of rice, and the foliar inhibitor could further inhibit the transport of Cd in rice plants, reducing the accumulation of Cd in rice deeply.
Soil Heavy Metal Pollution
