Bioavailability assessments following biochar and activated carbon amendment in DDT-contaminated soil.

The effects of 2.8% w/w granulated activated carbon (GAC) and two types of biochar (Burt's and BlueLeaf) on DDT bioavailability in soil (39 µg/g) were investigated using invertebrates (Eisenia fetida), plants (Cucurbita pepo spp. pepo) and a polyoxymethylene (POM) passive sampler method. Biochar significantly reduced DDT accumulation in E. fetida (49%) and showed no detrimental effects to invertebrate health. In contrast, addition of GAC caused significant toxic effects (invertebrate avoidance and decreased weight) and did not significantly reduce the accumulation of DDT into invertebrate tissue. None of the carbon amendments reduced plant uptake of DDT. Bioaccumulation of 4,4'DDT and 4,4'-DDE in plants (C. pepo spp. pepo) and invertebrates (E. fetida) was assessed using bioaccumulation factors (BAFs) and compared to predicted bioavailability using the freely-dissolved porewater obtained from a polyoxymethylene (POM) equilibrium biomimetic method. The bioavailable fraction predicted by the POM samplers correlated well with measured invertebrate uptake (<50% variability), but was different from plant root uptake by 134%. A literature review of C. pepo BAFs across DDT soil contamination levels and the inclusion of field data from a 2.5 µg/g DDT-contaminated site found that these plants exhibit a concentration threshold effect at [DDT](soil) > 10 µg/g. The results of these studies illustrate the importance of including plants in bioavailability studies as the use of carbon materials for in situ contaminant sorption moves from predominantly sediment to soil remediation technologies.

Physical, chemical and biological characterization of six biochars produced for the remediation of contaminated sites.

The physical and chemical properties of biochar vary based on feedstock sources and production conditions, making it possible to engineer biochars with specific functions (e.g. carbon sequestration, soil quality improvements, or contaminant sorption). In 2013, the International Biochar Initiative (IBI) made publically available their Standardized Product Definition and Product Testing Guidelines (Version 1.1) which set standards for physical and chemical characteristics for biochar. Six biochars made from three different feedstocks and at two temperatures were analyzed for characteristics related to their use as a soil amendment. The protocol describes analyses of the feedstocks and biochars and includes: cation exchange capacity (CEC), specific surface area (SSA), organic carbon (OC) and moisture percentage, pH, particle size distribution, and proximate and ultimate analysis. Also described in the protocol are the analyses of the feedstocks and biochars for contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), metals and mercury as well as nutrients (phosphorous, nitrite and nitrate and ammonium as nitrogen). The protocol also includes the biological testing procedures, earthworm avoidance and germination assays. Based on the quality assurance / quality control (QA/QC) results of blanks, duplicates, standards and reference materials, all methods were determined adequate for use with biochar and feedstock materials. All biochars and feedstocks were well within the criterion set by the IBI and there were little differences among biochars, except in the case of the biochar produced from construction waste materials. This biochar (referred to as Old biochar) was determined to have elevated levels of arsenic, chromium, copper, and lead, and failed the earthworm avoidance and germination assays. Based on these results, Old biochar would not be appropriate for use as a soil amendment for carbon sequestration, substrate quality improvements or remediation.

In situ application of activated carbon and biochar to PCB-contaminated soil and the effects of mixing regime.

The in situ use of carbon amendments such as activated carbon (AC) and biochar to minimize the bioavailability of organic contaminants is gaining in popularity. In the first in situ experiment conducted at a Canadian PCB-contaminated Brownfield site, GAC and two types of biochar were statistically equal at reducing PCB uptake into plants. PCB concentrations in Cucurbita pepo root tissue were reduced by 74%, 72% and 64%, with the addition of 2.8% GAC, Burt's biochar and BlueLeaf biochar, respectively. A complementary greenhouse study which included a bioaccumulation study of Eisenia fetida (earthworm), found mechanically mixing carbon amendments with PCB-contaminated soil (i.e. 24 h at 30 rpm) resulted in shoot, root and worm PCB concentrations 66%, 59% and 39% lower than in the manually mixed treatments (i.e. with a spade and bucket). Therefore, studies which mechanically mix carbon amendments with contaminated soil may over-estimate the short-term potential to reduce PCB bioavailability.

The use of biochar to reduce soil PCB bioavailability to Cucurbita pepo and Eisenia fetida.

Biochar is a carbon rich by-product produced from the thermal decomposition of organic matter under low oxygen concentrations. Currently many researchers are studying the ability of biochar to improve soil quality and function in agricultural soils while sustainably sequestering carbon. This paper focuses on a novel but complimentary application of biochar - the reduced bioavailability and phytoavailability of organic contaminants in soil, specifically polychlorinated biphenyls (PCBs). In this greenhouse experiment, the addition of 2.8% (by weight) biochar to soil contaminated with 136 and 3.1 µg/g PCBs, reduced PCB root concentration in the known phytoextractor Cucurbita pepo ssp. pepo by 77% and 58%, respectively. At 11.1% biochar, even greater reductions of 89% and 83% were recorded, while shoot reductions of 22% and 54% were observed. PCB concentrations in Eisenia fetida tissue were reduced by 52% and 88% at 2.8% and 11.1% biochar, respectively. In addition, biochar amended to industrial PCB-contaminated soil increased both aboveground plant biomass, and worm survival rates. Thus, biochar has significant potential to serve as a mechanism to decrease the bioavailability of organic contaminants (e.g. PCBs) in soil, reducing the risk these chemicals pose to environmental and human health, and at the same time improve soil quality and decrease CO(2) emissions.