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Session- Heavy Metals

 

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Use of Tailor-Made Fe and Mn Rich Composted Biosolids or Manure to Remediate Metal Contaminated Soils

 

CHANEY, RUFUS L. (1), Kukier, Urszula (2), Davis, Allen P. (3), Brown, Sally L. (4) and Ryan, James A. (5)

 

1. USDA-ARS-Animal Manure and Byproducts Lab, Beltsville, MD, 2. Virginia Tech, Blacksburg, VA, 3. University of Maryland, College Park, MD, University of Washington, Seattle, WA, US-Environmental Protection Agency, Cincinnati, OH, USA

 

In research to characterize the long term fate and phytoavailability of metals in soils, we have shown that Fe and Mn oxides play an important role in limiting solubility and availability of soil metals. We will report work on the effect of biosolids properties on the long term phytoavailability of soil Cd and Zn, and on new work which examines addition of byproduct Fe and Mn oxides to organic materials before anaerobic digestion or composting to see if we can convert low surface area Fe and Mn oxides into high surface area oxides which can better adsorb soil and compost metals. There are several possible benefits of enriching compost with adsorbent oxides, both for use as a micronutrient fertilizer, and as a remediation soil amendment. Using mixtures of composts rich in Fe and byproduct limestone materials, we have achieved effective remediation of Zn or Ni phytotoxic soils, and reduced plant uptake of Zn, Cd, Pb, Ni, etc., and bioavailability of Pb in amended soils. These are all part of the "Tailor Made Compost" concept -- to improve fertilizer and metal sorption ability using byproducts. The paper will also serve to review/update risk assessments for metals in composts and compost-amended soils. We have made remarkable progress in clarifying risks from Cd; malnutrition induced by subsistence rice consumption caused people to absorb much higher fraction of diet Cd than people who consume other foods. This was partly due to the absence of Zn transport to rice grain, but mainly due to deficient Fe, Zn and Ca for human nutrition. The implications of these findings are that when composts have normal Cd:Zn ratios (<0.01), no amount of Cd is a food-chain risk except thru flooded rice or tobacco. Composts commonly have Cd:Zn ratios < 0.005, offering excellent protection against soil Cd risks. This progress should remove concerns about Cd in composts. Further, by enriching Fe and Mn in compost products, the ability of the amended soil to adsorb metals is increased, and coupled with reasonable soil pH management, aids in prevention or remediation of metal phytotoxic soils such as Zn-Pb-smelter contaminated soils. We believe that the multiple demonstrations of remediation of Zn-toxic soils we have made in recent years shows a new market for Tailor Made Fe and Mn rich biosolids or manure composts.

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The Role of Compost in the Overall Introduction Process for Heavy Metals Into Soils

 

Kranert, MARTIN; Fruth, Frauke

 

(1) University of Applied Sciences Braunschweig/Wolfenbuettel, Institute for Waste Management and Environmental Monitoring, Germany

 

The application of secondary-raw material-fertilisers like compost made from separate collected bio-waste is strongly regulated by lawful ordinances (e.g. bio-waste ordinance) particularly under the aspect of heavy metal input. In contrast input from farmyard manure, mineral-fertilisers and atmospheric precipitation is trivialised comparatively and regarded as inevitable. Regarding an integral contemplation, the different evaluation-standards underlying this situation are to be questioned. The role of heavy metal input from compost in comparison of the input from other fertilizers is to be shown. Goal should be to subject fertilisers like trade-fertilisers, farmyard manure and  secondary-raw material-fertilisers to an uniform proper evaluation. The relevant lawful regulations for bio waste, sewage sludge, fertilizers and soil conservation in Germany shall be shortly presented. The nutrient and pollutant data of the relevant fertilisers will be shown. It will be described, that the heavy metal freights are especially depending on the quantity of used fertilisers but not on the fertilisers themselves. By a calculation of average heavy metal freights on arable land by different fertilizers it shall be shown, that lawful regulations only for secondary raw material fertilisers are not according to an equal treatment of all fertilisers. Furthermore, different evaluation-models for the use of fertilisers which are in the present discussion will be described. Differences between the models especially regarding the handling and transferability to the different kinds of fertilisers shall be shown and discussed.