Best practices for the remediation of soils impacted by cadmium and other heavy metals. Abimbola Abiola IICA Delegation in Haiti

Transcription

1 Best practices for the remediation of soils impacted by cadmium and other heavy metals Abimbola Abiola IICA Delegation in Haiti

2 Outlines Heavy metals of concern Proccesses Prevention Availability Removal Biological

3 Heavy Metals of Concern As Be Cd Cr Cu Hg Ni Pb Se Zn

4 Control - Avoid Soil Degradation Accumulations are more common in degraded soils Symptoms of soil degradation ph changes Low organic matter Low WHC Salinity Poor drainage High bulk density Erosion

5 Control Methods Stop additional introduction into the environment Avoid the use of phosphate based fertilizers High Cd content Affected by the source of the phosphate rock Sedimentary deposits are generally higher 21 ppm (1-150) Igneous deposits 2 ppm (1-4) Additions build up Cd and other heavy metals in the soil Avoid using contaminated water Water analysis is critical when water is used for irrigation Avoiding post-harvest contamination

6 Test Soil Deficiency of some macro or micro nutrients may lead to the accumulation of some heavy metals For example Low Zn may lead to accumulation of Cd

7 Availability Affected by the physical and chemical conditions Total Available Major factors ph acidic conditions leads to ionization of many heavy metals including Cd Cation Exchange Capacity High CEC attracts and binds cations

8 Organic Matter Increases Cation Exchange Capacity (CEC) Supplies nutrients to microorganisms and plants Health of plants depend on populations of microorganisms in its rhizosphere (root zone) Increases water holding capacity Increases infiltration of water in the soil Improves soil s ability to resist compaction Reduces erosion

9 Impacts of Compost on Mine Tailings Nickel Mine Tailings Amended Nickel Mine Tailings

10 Caution With Organic Matter It is stabilized e.g. compost Use properly cured and matured compost Proper C:N ratio < 25:1 Higher C:N ration may affect N availability Low in Cd and other heavy metals Category A compost is recommended Be careful with biosolids compost Use of biochar may reduce N availability

11 Kammann et al,

12 Cations and Cation Exchange Capacity Cation exchange capacity (CEC) is the total capacity of a soil to hold exchangeable cations. CEC is an inherent soil characteristic and is difficult to alter significantly. It influences the soil s ability to hold onto essential nutrients and provides a buffer against soil acidification. Soils with a higher clay fraction tend to have a higher CEC. Organic matter has a very high CEC. Sandy soils rely heavily on the high CEC of organic matter for the retention of nutrients in the topsoil

13 ph Decrease in soil ph increases available Cd Liming Liming rate Organic matter

14 Soil ph of Reclaimed Mine Tailings 1 year after Treatment Rank Name Mean n Non-sig. ranges CompAsh a 2 Comp a 3 CompLime a 4 CompNPK a 5 Lime b 6 Cont b LSD 0.05=0.7157

15 How Soils Become Acidic (Iowa State University) Nitrification of ammonium Bases removed by crops Bases removed by leaching Acidic parent material Carbonic acid from microbial and plant respiration Organic acids secreted by plant roots Precipitation Oxidation of sulfide

16 Steps in Making Limestone Recommendations Check soil ph Is lime needed? Determine CaCO3 requirement Use Buffer ph Function of the type of soil Adjust rate for limestone quality ECCE per ton or % (Effective CaCO 3 Equivalence) Adjust rate for incorporation depth Many online calculators eg.

17 Limestone Needed to Offset Acidity from Nitrogen Fertilizers Nitrogen Source Pound of Aglime per Pound of N Ammonium Sulfate 7 Ammonium Phosphates 7 Anhydrous Ammonia 4 Urea 4 28% Solution 4 Ammonium Nitrate 4 Approximate amount. Adapted from Modern Corn Production. US

18 Removal Hyperaccumulator A plant ability to grow on soils and to accumulate extraordinarily high amounts of heavy metals, in excess of the levels found in the majority of other species, without suffering phytotoxic effects Phytoextraction manipulation of the soil condition for maximizing the use of hyperaccumulator to remove contaminants from the soil Many hyperaccumulators for Cd also accumulate for other heavy metals e.g. Cr, Cu, Cs, Hg, Pb, Sr and Zn

19 Examples of hyperaccumulators for Cd Athyrium yokoscense Japanese spleenwort Avena strigose Bristle oats Brassicaceae - Mustards B. Juncea Indian mustard Helianthus annuus Sunflower Salix viminalis L. Basket willow Thlaspi caerulescens- Alpine pennycress Amaranthus retroflexus Redroot amaranth Vallisneria spiralis Eel Grass Nicotiana tabacum - Tobacco EPA, 2000 EPA/600/R-99/107

20 Caution with Hyperaccumulators Understand which part of the plants that accumulate the heavy metal Biomass must be harvested and removed Do not compost biomass for reuse on the plantation

21 Soil Washing This is possible but not a sustainable option Will involve acidification, washing and liming Nutrient and organic matter losses

22 Biology Selection and cultivation of varieties that do not accumulate Cd or other heavy metals

23 Questions?

24