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ARS Home » Southeast Area » Stuttgart, Arkansas » Dale Bumpers National Rice Research Center » Research » Publications at this Location » Publication #324750

Title: Arsenic uptake in organic rice production systems

item McClung, Anna
item Duke, Sara
item DUO, FUGEN - Texas A&M Agrilife
item ZHOU, XIN-GEN - Texas A&M Agrilife
item Chaney, Rufus
item GERADS, RUSS - Applied Speciation And Consulting, Llc

Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/23/2015
Publication Date: 7/2/2017
Citation: McClung, A.M., Duke, S.E., Duo, F., Zhou, X., Chaney, R.L., Gerads, R. 2017. Arsenic uptake in organic rice production systems. Proc. 36th Rice Technical Working Group Meeting, Galveston, TX, p.42-43. March 1-4, 2016. CDROM.

Interpretive Summary:

Technical Abstract: Arsenic in rice is known to be a problem in some rice-producing countries that have high levels of inorganic arsenic naturally occurring in water resources. However, it was never considered an issue for USA produced rice until international market surveys were published, indicating some USA rice samples were high in total arsenic content (a combination of inorganic and organic forms of arsenic). Since that time, an international limit of 0.200 ppm of inorganic arsenic (iAs), considered the toxic form for humans, in milled rice has been established. Some of the USA rice samples that were found to have high total arsenic had been produced under organic management systems. This was of concern to the organic industry as consumers consider organically produced foods to be safe and pesticide free. To address this issue, we conducted a series of studies to determine the impact of several organic cultural management practices on arsenic accumulation in rice. Replicated field trials were conducted at Beaumont, TX during 2009-2013 on land that had been maintained under certified organic practices. Studies were conducted to evaluate the impact of variety, organic fertilizer product, fertilizer rate, and green manure crop on grain arsenic accumulation. In a cultivar study conducted over 3 years on conventionally (following 2 years fallow) and organically managed land (following winter green manure crops), we found similar levels of total arsenic (TAs) in brown rice between the two systems, 0.51 and 0.59 ppm, respectively. However, higher levels of TAs in milled rice were found under organic management (0.58 ppm) than under conventional management (0.39 ppm). Speciation analysis demonstrated that iAs contents were quite similar between the organic and conventional systems (0.15 and 0.18 ppm, respectively) and were relatively stable over years, but the organically -produced rice had much higher levels of organic forms of arsenic (oAs, DMA and MMA) which fluctuated over years. These results indicated the importance of assessing iAs through speciation analysis and not relying solely on TAs analysis as oAs contents can vary considerably. Thus, speciation was performed on milled rice of 7 of the 14 cultivars that were ranked low, intermediate and high in TAs. Varieties were very similar in iAs contents but differed significantly in oAs contents. The allelopathic germplasm PI 338046 had the highest iAs under the organic management system, whereas Sierra and Colorado had the lowest. Of the 7 cultivars, there was a positive association of iAs and oAs contents with yield, plant height, maturity, and length of grainfill. Six organic fertilizer products were compared in 2010. When applied at the same N level they did not differ in yield or TAs. One exception to this was Maxim Compost which produced significantly lower TAs and lower yield. This formulation had much higher phosphorus (3-10-1.5, N-P-K) than the other products and P is known to compete with As at cellular transport sites. As compared to the control (no fertilizer applied), there was a trend for increasing rates of fertilizer under organic management to increase yields and milled rice As accumulation, however this was not always significant. In all of the studies, year of production (includes weather, previous cropping history, and field site) explained most of the variability in yield and As accumulation. In general, higher yielding environments, whether a result of controlled (cultural) or uncontrolled (weather) effects, tended to result in higher As accumulation and was primarily driven by oAs. These results suggest that efforts to increase the nutrient value of the soil through green manure crops and/or organic fertilizer amendments may enhance microbial activity in the soil that make oAs more available for uptake by the plant but have little impact on iAs uptake. Our research