Phosphorus-cadmium interactions in paddy soils

Seshadri, B.,Bolan, N.S.,Wijesekara, H.,Kunhikrishnan, A.,Thangarajan, R.,Qi, F.,Matheyarasu, R.,Rocco, C.,Mbene, K.,Naidu, R. Elsevier Scientific Pub. Co 2016 Geoderma Vol.270 No.-

<P>Regular application of phosphate (P) fertilisers has been identified as the main source of heavy metal(loid) contamination including cadmium (Cd) in agricultural soils. Some of these P fertilisers that act as a source of Cd contamination of soils have also been found to act as a sink for the immobilisation of this metal(loid). In paddy soils, redox reactions play an important role in the (im)mobilisation of nutrients and heavy metal(loid)s, as a result of flooding of the rice plains. Although a number of studies have examined the potential value of P compounds in the immobilisation of metals in contaminated soils, there has been no comprehensive review on the mechanisms involved in the P-induced (im)mobilisation of Cd in paddy soils. There are a number of factors that influences P induced Cd (im)mobilisation in paddy soils that include pH, redox reactions, liming effect, rhizosphere acidification and root iron plaques. Following a brief overview of the reactions of Cd and common P compounds that are used as fertiliser in soils, the review focuses on the above mentioned mechanisms for the (im)mobilisation of Cd by P compounds in paddy soils. The role of iron plaques on Cd status in soil and rice plants is also discussed followed by a summary and future research needs. (C) 2015 Elsevier B.V. All rights reserved.</P>

Recycled water sources influence the bioavailability of copper to earthworms

Kunhikrishnan, A.,Bolan, N.S.,Naidu, R.,Kim, W.I. Elsevier Scientific Pub. Co 2013 Journal of hazardous materials Vol.261 No.-

Re-use of wastewaters can overcome shortfalls in irrigation demand and mitigate environmental pollution. However, in an untreated or partially treated state, these water sources can introduce inorganic contaminants, including heavy metals, to soils that are irrigated. In this study, earthworms (Eisenia fetida) have been used to determine copper (Cu) bioavailability in two contrasting soils irrigated with farm dairy, piggery and winery effluents. Soils spiked with varying levels of Cu (0-1000mg/kg) were subsequently irrigated with recycled waters and Milli-Q (MQ) water and Cu bioavailability to earthworms determined by mortality and avoidance tests. Earthworms clearly avoided high Cu soils and the effect was more pronounced in the absence than presence of recycled water irrigation. At the highest Cu concentration (1000mg/kg), worm mortality was 100% when irrigated with MQ-water; however, when irrigated with recycled waters, mortality decreased by 30%. Accumulation of Cu in earthworms was significantly less in the presence of recycled water and was dependent on CaCl<SUB>2</SUB>-extractable free Cu<SUP>2+</SUP> concentration in the soil. Here, it is evident that organic carbon in recycled waters was effective in decreasing the toxic effects of Cu on earthworms, indicating that the metal-organic complexes decreased Cu bioavailability to earthworms.

Remediation of heavy metal(loid)s contaminated soils - To mobilize or to immobilize?

Bolan, N.,Kunhikrishnan, A.,Thangarajan, R.,Kumpiene, J.,Park, J.,Makino, T.,Kirkham, M.B.,Scheckel, K. Elsevier Scientific Pub. Co 2014 Journal of hazardous materials Vol.266 No.-

Unlike organic contaminants, metal(loid)s do not undergo microbial or chemical degradation and persist for a long time after their introduction. Bioavailability of metal(loid)s plays a vital role in the remediation of contaminated soils. In this review, the remediation of heavy metal(loid) contaminated soils through manipulating their bioavailability using a range of soil amendments will be presented. Mobilizing amendments such as chelating and desorbing agents increase the bioavailability and mobility of metal(loid)s. Immobilizing amendments such of precipitating agents and sorbent materials decrease the bioavailabilty and mobility of metal(loid)s. Mobilizing agents can be used to enhance the removal of heavy metal(loid)s though plant uptake and soil washing. Immobilizing agents can be used to reduce the transfer to metal(loid)s to food chain via plant uptake and leaching to groundwater. One of the major limitations of mobilizing technique is susceptibility to leaching of the mobilized heavy metal(loid)s in the absence of active plant uptake. Similarly, in the case of the immobilization technique the long-term stability of the immobilized heavy metal(loid)s needs to be monitored.

Sorption-bioavailability nexus of arsenic and cadmium in variable-charge soils

Bolan, N.,Mahimairaja, S.,Kunhikrishnan, A.,Naidu, R. Elsevier Scientific Pub. Co 2013 Journal of hazardous materials Vol.261 No.-

In this work, the nexus between sorption and bioavailability of arsenic (As) and cadmium (Cd) as affected by soil type, soil pH, ageing, and mobilizing agents were examined. The adsorption of As and Cd was examined using a number of allophanic and non-allophanic soils which vary in their charge components. The effect of pH and ageing on the bioavailability of As and Cd was examined using spiked soils in a plant growth experiment. The effect of phosphate (P)-induced mobility of As on its bioavailability was examined using a naturally contaminated sheep dip soil. The results indicated that the adsorption of both As and Cd varied amongst the soils, and the difference in Cd adsorption is attributed to the difference in surface charge. An increase in soil pH increased net negative charge by an average of 45.7mmol/kg/pH thereby increasing cation (Cd) adsorption; whereas, the effect of pH on anion (As) adsorption was inconsistent. The bioavailability of As and Cd decreased by 3.31- and 2.30-fold, respectively, with ageing which may be attributed to increased immobilization. Phosphate addition increased the mobility and bioavailability of As by 4.34- and 3.35-fold, respectively, in the sheep dip soil. However, the net effect of P on As phytoavailability depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots. The results demonstrate the nexus between sorption and bioavailability of As and Cd in soils, indicating that the effects of various factors on bioavailability are mediated through their effects on sorption reactions.

Amelioration of Horticultural Growing Media Properties Through Rice Hull Biochar Incorporation

Kim, H. S.,Kim, K. R.,Yang, J. E.,Ok, Y. S.,Kim, W. I.,Kunhikrishnan, A.,Kim, K. H. Springer Science + Business Media 2017 Waste and biomass valorization Vol.8 No.2

<P>The current study was conducted in order to examine the applicability of rice hull derived biochar (BC) to improve the properties of growing media (GM). Biochar was incorporated into a growing media composed of coir dust, perlite and vermiculite at 0, 1, 2 and 5 % (w/w). Subsequently, the physicochemical properties of the GM-BC mixtures were determined in the cultivation of kale (Brassica oleracea L. var. acephala) for 25 days through the observation of the plant growth response. During kale cultivation in the GM-BC mixtures, the leachates were collected and analyzed to determine the changes in nutrient levels due to BC amendment. Application of rice hull-derived BC increased the retention of nutrients in the growing media due to a biochar-induced increase in cation exchange capacity, in addition to the biochar nutrient supply such as potassium and phosphorus. Furthermore, a higher water content of the growing media was observed when BC was used as an amendment, mainly due to the increased proportion of pore space available for water storage. The growth rate of kale was also increased as the biochar incorporation rate was increased. For example, the dry weight of the kale shoots was 150 % higher when grown in media containing 5 % GM-BC mixture than with the control growing media (with no biochar). From these results, it can be concluded that the rice hull-derived biochar would be a practically applicable amendment to improve the properties of the growing media.</P>

논토양 비소의 토양위해성 저감화 연구동향

김원일,고우리,A. Kunhikrishnan,류지혁,정구복,김지영,김권래,조남준 한국토양비료학회 2014 한국토양비료학회 세미나 Vol.2014 No.8

Differential effect of biochar upon reduction-induced mobility and bioavailability of arsenate and chromate

Choppala, G.,Bolan, N.,Kunhikrishnan, A.,Bush, R. Pergamon Press 2016 CHEMOSPHERE - Vol.144 No.-

Heavy metals such as chromium (Cr) and arsenic (As) occur in ionic form in soil, with chromate [Cr(VI)] and arsenate As(V) being the most pre-dominant forms. The application of biochar to Cr(VI) and As(V) spiked and field contaminated soils was evaluated on the reduction processes [(Cr(VI) to Cr(III)] and [As(V) to As(III))], and subsequent mobility and bioavailability of both As(V) and Cr(VI). The assays used in this study included leaching, soil microbial activity and XPS techniques. The reduction rate of As(V) was lower than that of Cr(VI) with and without biochar addition, however, supplementation with biochar enhanced the reduction process of As(V). Leaching experiments indicated Cr(VI) was more mobile than As(V). Addition of biochar reversed the effect by reducing the mobility of Cr and increasing that of As. The presence of Cr and As in both spiked and contaminated soils reduced microbial activity, but with the addition of biochar to these soils, the microbial activity increased in the Cr(VI) contaminated soils, while it was further decreased with As(V) contaminated soils. The addition of biochar was effective in mitigating Cr toxicity by reducing Cr(VI) to Cr(III). In contrast, the conversion process of As(V) to As(III) hastened by biochar was not favourable, as As(III) is more toxic in soils. Overall, the presence of functional groups on biochar promotes reduction by providing the electrons required for reduction processes to occur as determined by XPS data.

Co-composting solid biowastes with alkaline materials to enhance carbon stabilization and revegetation potential

Chowdhury, S.,Bolan, N. S.,Seshadri, B.,Kunhikrishnan, A.,Wijesekara, H.,Xu, Y.,Yang, J.,Kim, G. H.,Sparks, D.,Rumpel, C. ECOMED PUBLISHERS 2016 Environmental Science and Pollution Research Vol.23 No.8

<P>Co-composting biowastes such as manures and biosolids can be used to stabilize carbon (C) without impacting the quality of these biowastes. This study investigated the effect of co-composting biowastes with alkaline materials on C stabilization and monitored the fertilization and revegetation values of these co-composts. The stabilization of C in biowastes (poultry manure and biosolids) was examined by their composting in the presence of various alkaline amendments (lime, fluidized bed boiler ash, flue gas desulphurization gypsum, and red mud) for 6 months in a controlled environment. The effects of co-composting on the biowastes' properties were assessed for different physical C fractions, microbial biomass C, priming effect, potentially mineralizable nitrogen, bioavailable phosphorus, and revegetation of an urban landfill soil. Co-composting biowastes with alkaline materials increased C stabilization, attributed to interaction with alkaline materials, thereby protecting it from microbial decomposition. The co-composted biowastes also increased the fertility of the landfill soil, thereby enhancing its revegetation potential. Stabilization of biowastes using alkaline materials through co-composting maintains their fertilization value in terms of improving plant growth. The co-composted biowastes also contribute to long-term soil C sequestration and reduction of bioavailability of heavy metals.</P>

Cadmium Contamination and Its Risk Management in Rice Ecosystems

Bolan, N.S.,Makino, T.,Kunhikrishnan, A.,Kim, P.-J.,Ishikawa, S.,Murakami, M.,Naidu, R.,Kirkham, M.B. ACADEMIC PRESS 2013 Advances in agronomy Vol.119 No.-

농업환경 및 농산물 중 비소오염 연구동향

김원일 ( Won Il Kim ),이지호 ( Ji Ho Lee ),( A. Kunhikrishnan ),고우리 ( Woo Ri Go ),이정미 ( Jeong Mi Lee ),백민경 ( Min Kyoung Paik ),류지혁 ( Ji Hyock Yoo ),김지영 ( Ji Young Kim ) 한국환경농학회 2012 한국환경농학회 학술대회집 Vol.2012 No.-

농촌진흥청 및 환경부의 폐금속 광산인근 농경지 중금속 오염 모니터링에서 비소에 의한 오염이 상당수 확인되고 있고, 또한 코덱스오염물질분과위원회에서는 2010년부터 쌀의 비소기준 설정을 위한 논의가 계속되고 있어 농업환경 및 농산물에 대한 비소 관리가 시급한 실정이다. 이에 따라 본 발표에서는 우리나라 농업환경 및 농산물의 비소오염 기준설정, 모니터링, 환경 위해성 및 독성, 작물로의 흡수이행, 복원을 통한 오염 저감화에 대한 화학물질안전과 무기화학연구실에서 수행한 현재까지의 현황 및 연구동향을 소개하고자 한다. 본 초록에서는 2009년부터 2010년까지 수행한 우리나라 폐금속 광산인근 지역에서의 비소오염 현황 및 환경위해성 평가 결과에 대해서만 언급하고자 한다. 국내 24지점의 폐광산 주변 지역에서 논토양, 용수 및 재배된 쌀의 비소 오염도를 조사하였고, 인체에 대한 평균 일일 노출량(ADD)을 산정하여 발암 위해 확률을 평가하였다. 광산인근에서 재배된 쌀 중 총 비소의 평균 농도는 0.123 mg/kg으로 조사되었다. ADD값은 총 비소농도함량을 고려하여 FAO/WHO에서 정한 2.1 ㎍/kg b.w./day의 PTDI값을 초과하지 않았다. 그러나, 일부 폐광인근에서 재배한 쌀을 섭취했을 경우, 인체의 발암 위해 확률은 허용수준인 10-4 범위를 초과하였고, 따라서 비소로 오염된 쌀을 장기간 섭취하게 된다면 인체 독성영향의 가능성은 있는 것으로 판단된다. 이들 결과를 통하여 비소오염 논토양에 적절한 관리방안을 도출하고 안전농산물 생산에 기여할 것이다.