Soil and Water Sciences

Biography

Biography: Paula F Avila

Abstract

Trace metals in soil might have origin from anthropogenic sources as metal mining and processing. Soil acts as a metalloid reservoir considered dangerous due to their potential toxicity and persistence in the environment. Metalloids accumulation in soil can degrade its quality. Phytotechnologies use metal tolerant plants and microorganisms to extract, degrade, contain or immobilize metalloids in soil, promoting their restoration. Borralha mine (Portugal) explored tungsten; soil is contaminated with high metalloid concentrations and can benefit from phytotechnologies in its remediation and requalification. Energy crops such as sunflower (Helianthus annuus) and Populus sp., with high potential success to adapt to contaminated soil, assisted by microorganisms (mycorrhizal fungi and plant growth promoting bacteria) that stimulate crop growth, can benefit soil quality and functionality reducing the stress promoted by the contamination. Assessing the environmentally available concentrations and metalloids distribution in soil fractions was the first step in this study. Soil physico-chemical parameters: 52% sand, 42.4% silt, 2.1% clay; pH 5.0; 10.5% OM; 4.2% CO₃^2-, 0.11% N and 113 µS/cm EC. According to the proposed guidelines for Portuguese soil (in mg kg^-1 Cu=35; Cd=0.6; As=22; Pb=34 and Zn=85) Cu exceed 24 times de guideline value and Cd 15 times. Sequential chemical extraction: most pollutant fraction consists of metals bounded to sulfides and released under oxidizing conditions in AMD production, nevertheless, Cu and Cd were extracted with acetic acid suggesting linkage to the easily mobilized phases. Selective single extraction to assess bioavailability of metalloids according to the maximum permitted levels for water soluble forms of Cd=0.03 and Cu=0.7 mg kg⁻¹ extracted soluble concentrations of Cd and Cu (H₂0_Cd 3.7X, NH₄NO_3Cd 8.3X, EDTA_Cd 40X and H₂0_Cu 1.3X, NH₄NO_3Cu 15.7X, EDTA_Cu 407X) are above toxic levels revealing metal mobility; extraction capacity of metals followed the order of EDTA> NH₄NO₃>H₂O; the mobility and bioavailability of the metalloids declines as Cd>>Zn>Cu>Pb>As.

Figure 1: (a) Location of the study area (b) main geological units and (c) wind rose of the prevailing winds. Main sources of contamination: tailings (A, C, D) with huge volumes and pond (B) with rejected muds and slush discharged from the ore process. 1) experimental area for phytotechnologies studies and 2) delimited Sunflower and Populus plots where soil was collected.