ANALYTICAL SCIENCES MAY 2020, VOL. 36 531 2020 © The Japan Society for Analytical Chemistry Original Papers Variations in Cadmium Concentrations in Rice and Oxidation- Reduction Potential at the Soil Surface with Supplementation of Fermented Botanical Waste-based Amendment in Large-scale Farmland Nobuhiko WADA,*1,*2 Gao DI,*1 Hideyuki ITABASHI,*1 Masanobu MORI,*3† Yusuo LIN,*4 Shaopo DENG,*4 Weiwei XU,*5 Weiwei GUO,*6 Yuanheng LUO,*6 and Dianyu ZHU*7 *1 Graduate School of Science and Technology, Gunma University, 1-5-1, Tenjin-cho, Kiryu 376–8515, Japan *2 Shanghai Shenglong Environment Remediation Materials, Co. Ltd, Building 6, No. 936, Guoshun Road, Nanqiao Town, Fengxian District, Shanghai 201400, China *3 Faculty of Science and Technology, Kochi University, 2-5-1 Akebono-cho, Kochi 780–8520, Japan *4 Nanjing Institute of Environmental Science, MEP, P. R. China, Jiangwangmiao Road 8, Xuanwu District, Nanjing, Jiangsu Province 210042, China *5 Geological Survey of Jiangsu Province, 700 Zhujiang Road, Xuanwu District, Nanjing, Jiangsu Province 210018, China *6 Shanghai Shenglong Environment Remediation Technologies, Co. Ltd, Floor 13, Building No. 2, 100 Qinzhou Road, Xuhui District, Shanghai 200235, China *7 School of the Environment, Nanjing University, 163 Xianlin Road, Qixia District, Nanjing, Jiangsu Province 210023, China We monitored the relationship between the cadmium (Cd) concentration uptake of rice and the oxidation-reduction potential (ORP) at the soil surface with the supplementation of fermented botanical waste-based amendment (FBWA), an organic fertilizer prepared from woody and food wastes. This study was carried out for 3 years in the western part of Jiangsu Province, China. It was found that the Cd concentration taken up by rice was correlated to a decreased the ORP of the cultivated soil. The yield of rice was ∼1.20 times higher than that of the control plot. The effects of reducing the Cd content in rice and increasing the rice yield remained for 2 years after FBWA application. Finally, Cd was immobilized in the soil with adsorption to FBWA or the decomposed products. The ORP measurement during rice cultivation might be a key index to predict the suppression effect of Cd uptake into the rice or limitation of the sustainable effect by the FBWA. Keywords Cadmium, rice, reduction, farmland, amendment, soil analysis (Received October 5, 2019; Accepted March 3, 2020; Advance Publication Released Online by J-STAGE March 13, 2020) Land and Resources10 conducted the Geological Survey of Introduction China and measured pollutant levels in farmlands, forestlands, and unused land. Overall, 16.1% of the sampled locations had The cadmium (Cd) uptake by rice grown in Cd-contaminated contaminant levels exceeding thresholds established by the soils is a serious problem worldwide. In Thailand,1 Vietnam,2 Environmental Quality Standard for Soils (GB 15618-1995). Bangladesh,3 Pakistan,4 and China,5 researchers have investigated Therefore, cultivation methods for reducing the Cd contamination the potential health risks of ingesting rice harvested from in rice have mainly been developed in Japan and China. These Cd-contaminated soils. All studies emphasized the need for include autoclaved lightweight-concrete (ALC), which contains measures to mitigate Cd contamination. Excessive Cd causes calcium silicate;11 inorganic adsorbent added to farmland soil genetic instability in living organisms and inhibits plant growth.6 during irrigation;12 biochar soil amendment (BSA) composed of In agroecosystems, genotoxic compounds significantly decrease hay, wood chips, sawdust, or cereal straw waste;13–29 or a mixture the crop yield and quality.4,7,8 In Japan in 1955, illness was of cedar bark, rice bran, and soybean waste.30 reported in persons who consumed rice cultivated on soil The immobilization of Cd in soil might effectively suppress irrigated with Cd-contaminated river water.9 crop Cd uptake. However, spraying industrial or food wastes China is the largest producer and consumer of rice in the onto soils often decreases the crop yield because it causes world. From April 2005 to December 2013, the Ministry of irrigation water eutrophication, which inhibits plant growth. Therefore, a practical cultivation method is needed that both † To whom correspondence should be addressed. reduces rice Cd uptake and maintains high yields in Cd- E-mail: [email protected] contaminated farmlands. 532 ANALYTICAL SCIENCES MAY 2020, VOL. 36 In the present study, we ameliorated Cd-contaminated soil by The pH of soil suspensions and water samples were determined applying fermented botanical waste-based amendment (FBWA) using a pH meter (pH scan20, Bante Instruments, Shanghai, consisting of locally sourced decomposing bark sawdust, China; PB-21, Sartorius, Göttingen, Germany; and D-72, hardwood stems, tofu waste sludge, and rice bran. These Horiba, Kyoto, Japan). The ORP of these samples was obtained materials were broken down with white rot fungus. Lignin, using an ORP tester (ORPscan20, Bante Instruments, Shanghai, which constitutes 20 – 35% of the cell walls of coniferous China; and D-72, Horiba, Kyoto, Japan). woody bark and sawdust (the main raw materials of FBWA), is The cation-exchange capacity (CEC) in the FBWA was known to adsorb heavy metals, such as Cd.31–34 However, even measured by using the barium acetate method (Measurement if applying woody bark alone to the soil, the decomposition is Act #51 1992). The phosphorus (P) and potassium (K) were slow and takes a long time to assimilate into the soil. Therefore, analyzed in the oxidant by using energy dispersion X-ray we mixed rice bran (an agricultural residue) and okara (the fluorescence (ED-XRF) at JBCA (Japan Bark Compost strained lees of tofu) with bark at equal weight. They play the Association). The pH and the ORP of the paddy soil and water role as a forcing bed for white-rot fungi added to decompose the were measured both before and after spraying with FBWA. bark. The fungi actively decomposes bark by consuming any Aqueous soil suspensions were collected in 180-mL plastic cups waste products. and left to stand 1 min before any pH and ORP determinations. Several studies have reported the suppression of Cd The pH meter was calibrated at pH 4, 7, and 9. The ORP meter uptake by rice using amendments derived from industrial was calibrated using a standard solution manufactured by wastes.14,16,20,23,27,29,30 The applications of such amendments are Horiba (Kyoto, Japan). mostly conducted in Japan and China because rice is a staple food there. Table S1 in Supporting Information (SI) lists earlier Preparation of FBWA studies on the amendments used to reduce Cd in rice cultivated FBWA consisting of shredded bark sawdust and hardwood in Japan and China. However, most of the experiments listed stems, were obtained from moldy wood. Bean curd was are “pot studies” or small field-scale experiments. obtained from tofu manufacturing. Rice bran was obtained The present study was conducted concerning large-scale crop from rice polishing. All raw materials were purchased from cultivation on a 9636 m2 farmland continuously for 3 years. In industrial production facilities in China (undisclosed). Equal particular, we focused on whether the variation of the oxidation- quantities of bark, bean curd, and rice bran were mixed with reduction potential (ORP) related to that of the Cd concentration white rot fungus (consisting mainly of Phanerochaete in harvested brown rice, and clarify whether there was a positive chrysosporium) cultivated at Sasutera Co. Ltd. (Niigata, Japan). effect of FBWA addition. In our previous study, the Cd The mixture was fermented at 60 – 80°C for 7 d using only concertation in brown rice harvested in an organic amendment- white rot fungus. The final moisture content was 10%. supplied soil that provided a decrease of ORP in surface soil during rice cultivation was largely reduced compared with that Location of farmlands in soil without the amendment.30 Moreover, the rice yield in soil A schematic representation of the farmland in the present with FBWA supplementation was also observed in the current study is shown in Fig. 1. A field trial was conducted in the study because it is of practical importance to consider the effect western part of Jiangsu Province, China at ∼5 m altitude. Both of supplementation on plant growth. Furthermore, we rice and wheat were cultivated there annually. The area of the investigated the mass transfer of Cd from soil to brown rice experimental farmland was 9635.4 m2 (90.9 m E–W and using the concentration factor and the Cd uptake rate. 106.0 m N–S). The farmland was situated both east and west of a 20-m-wide canal. Several pottery and chemical factories are located to the south of the farmland (Fig. 1). Experimental The experimental farmland consisted of six plots (A–F) and an embankment passage 30–40 cm wide. For each plot, the soil Reagents, materials, and instruments and the rice plant samples were collected within the 1 × 1 m of All reagents were obtained from Wako Pure Chemical area of three equal parts (1 – 3) per each plot (A – F) as shown Industries, Ltd. (Osaka, Japan) or from Suzhou Crystal Chemical in Fig. 1. In detail, the rice plants were collected from the Co. Ltd. (Suzhou, China). Purified water was obtained from center and four corners in the area, and the soil samples were Merck Serono S.A.S. (Geneva, Switzerland) and from EUG- collected using a cylindrical stainless-steel soil sampler (35 mm CY2-20 (Nanjing YouGen Environmental Protection Technology diameter) at 15 cm depth from the center. Co. Ltd., Nanjing, China). Before evaluating the effect of FBWA spraying on the Cd Soil, water, and rice samples were analyzed at the Geological uptake in rice, the heavy metal concentration was measured in Survey of Jiangsu Province and at the School of the Environment, irrigation water pumped from canals adjacent to the farmland.