Allison Rutter

Potential for Phytoremediation of Polychlorinated Biphenyl-(PCB)-Contaminated Soil

Weathered soils contaminated with commercial-grade Aroclor 1260 from three sites in Canada were used to investigate the polychlorinated biphenyl (PCB) phytoextraction potential of nine plant species (Festuca arundinacea, Glycine max, Medicago sativa, Phalaris arundinacea, Lolium multiflorum, Carex normalis, and three varieties of Cucurbita pepo ssp. pepo) under controlled greenhouse conditions. The soils used varied in PCB concentration (90–4200 μg/g) and total organic content (0.06–2.02%). Greenhouse experiments controlled for PCB volatilization through the use of a vented enclosure and by isolating the contaminated soils with parafilm. After 8 wks, PCB concentrations of 47–6700 μg/g were observed in root tissues. Although PCB concentrations in shoot tissues were lower (<1–470 μg/g), the absolute amounts of PCBs observed in shoot tissue were significant (1.7–290 μg) once shoot biomass was accounted for. Congener signatures indicated that tetra-to hexa-chlorobiphenyls contributed the largest proportions to shoot tissues, but hepta-to nona-chorobiphenyls were also present in measurable amounts. Overall, the results indicate that varieties of C. pepo were more effective at extracting PCBs from soil than other plants screened. The evidence suggests that this was mainly due to root uptake of PCBs and tranlocation to the shoots, rather than volatilization of PCBs from soil. All plants screened showed signs of stress in the most highly contaminated soil (4200 μg/g), but not in the two lower PCB contaminated soils (250 and 90 μg/g, respectively). No detectable decreases in soil PCB concentrations were observed in these short-term greenhouse experiments, but the results suggest that this may be achievable through multiple plantings.

Extraction and speciation of arsenic in plants grown on arsenic contaminated soils

A sequential arsenic extraction method was developed that yielded extraction efficiencies (EE) that were approximately double those using current methods for terrestrial plants. The method was applied to plants from two arsenic contaminated sites and showed potential for risk assessment studies. In the method, plants were extracted first by 1:1 water-methanol followed by 0.1M hydrochloric (HCl) acid. Total arsenic in plant and soil samples collected from contaminated sites was mineralized by acid digestion and detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and hydride generation-atomic absorption spectrometry (HG-AAS). Arsenic speciation was done by high performance liquid chromatography coupled with HG-AAS (HPLC-HGAAS) and by HPLC coupled with ICP-mass spectrometry (HPLC-ICP-MS). Spike recovery experiments with arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) showed stability of the species in the extraction processes. Speciation analysis by X-ray absorption near edge spectroscopy (XANES) demonstrated that no transformation of As(III) and As(V) occurred due to sample handling. Dilute HCl was efficient in extracting arsenic from plants; however, extraction and determination of organic species were difficult in this medium. Sequential extraction with 1:1 water-methanol followed by 0.1M-HCl was most useful in extracting and speciating both organic and inorganic arsenic from plants. Trace amounts of MA and DMA in plants could be detected by HPLC-HGAAS aided by the process of separation and preconcentration of the sequential extraction method. Both organic and inorganic arsenic compounds could be detected simultaneously in synthetic gastric fluid extracts (GFE) but EEs by this method were lower than those of the sequential method. The developed sequential method was shown to be reliable and applicable to various terrestrial plants for arsenic extraction and speciation.

The effects of repeated planting, planting density, and specific transfer pathways on PCB uptake by Cucurbita pepo grown in field conditions

An in situ field investigation into the potential of PCB phytoextraction by Cucurbita pepo ssp. pepo (pumpkin) plants was continued for a second year at a field site known to be contaminated with a mixture of Aroclors 1254 and 1260 (average soil [PCB]=21 microg/g). Plant stem and leaf PCB concentrations in this second field season (11 and 8.9 microg/g, respectively) were observed to increase significantly from the stem and leaf PCB concentrations reported in the previous year (5.7 and 3.9 microg/g, respectively) while the total biomass produced as well as soil and plant root PCB concentrations did not change. Furthermore, the lower stems of some plants exhibited PCB concentrations as high as 43 microg/g, resulting in bioaccumulation factors (where BAF(plant part)=[PCB](plant part)/[PCB](soil)) for parts of the plant shoot as high as 2. Increased planting density was observed to significantly decrease both plant biomass and plant stem PCB concentrations (to 7.7 microg/g), but did not change plant root PCB concentrations. Finally, the results from this study provided further evidence that that under realistic field conditions, PCB transfer to pumpkin plants was primarily via root uptake and translocation. Other contaminant transfer pathways such as direct soil contamination, atmospheric deposition and volatilization from soil and subsequent redeposition on shoots appeared to have negligible contributions to overall pumpkin plant PCB burdens.

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.

Remediation of former military bases in the Canadian Arctic

Abstract This paper describes novel aspects of the remediation of three former military bases in the Canadian Arctic. At Iqaluit, the site has been totally cleaned up. All buildings were demolished, and soils contaminated with metals and polychlorinated biphenyls (PCBs) removed. Soils were excavated and most containerized and shipped south for disposal; soils containing 1–5 ppm PCBs were buried on site along with nonhazardous debris. PCB-contaminated concrete foundations were also investigated and removed. While most contamination was in the surface of the active layer, some migration of PCBs along the surface of the underlying bedrock at greater depth was found. At Sarcpa Lake, a dump leaching PCBs was excavated. Methodology was developed for this investigation and the difficulties of excavation in permafrost are described. The PCBs in the dump were from electrical equipment and/or PCB-containing paint used at this former Distant Early Warning (DEW) Line site. Investigation of the painted material at the site showed PCB levels as high as 7.4% in the paint. Wall swab results show that the repainting of the walls had effectively rendered the PCBs unavailable to solvent washing. At Resolution Island, the extent of contamination is much larger than the other two sites. Interceptor barriers were designed and installed in the leachate pathways carrying PCBs between the site and the ocean. At this site, the presence of petroleum products along the drainage pathway has led to increased transport of PCBs due to their higher solubility in these solvents as compared to water. Current progress at this unique remote site and the options for dealing with the contaminated soil are discussed.

Potential for phytoextraction of PCBs from contaminated soils using weeds.

A comprehensive investigation of the potential of twenty-seven different species of weeds to phytoextract polychlorinated biphenyls (PCBs) from contaminated soil was conducted at two field sites (Etobicoke and Lindsay) in southern Ontario, Canada. Soil concentrations were 31 microg/g and 4.7 microg/g at each site respectively. All species accumulated PCBs in their root and shoot tissues. Mean shoot concentrations at the two sites ranged from 0.42 microg/g for Chenopodium album to 35 microg/g for Vicia cracca (dry weight). Bioaccumulation factors (BAF=[PCB](plant tissue)/[PCB](mean soil)) at the two sites ranged from 0.08 for Cirsium vulgare to 1.1 for V. cracca. Maximum shoot extractions were 420 microg for Solidago canadensis at the Etobicoke site, and 120 microg for Chrysanthemum leucanthemum at the Lindsay site. When plant density was taken into account with a theoretical density value, seventeen species appeared to be able to extract a similar or greater quantity of PCBs into the shoot tissue than pumpkins (Curcurbita pepo ssp. pepo) which are known PCB accumulators. Therefore, some of these weed species are promising candidates for future phytoremediation studies.

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, Burts 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 absorption and translocation of polychlorinated biphenyl congeners by Cucurbita pepo ssp pepo.

The mobility of polychlorinated biphenyl (PCB) congeners within Cucurbita pepo ssp pepo cv. Howden (pumpkin), a PCB phytoextracting plant, was investigated through a comparison of field-weathered soil, root, shoot, and xylem sap congener profiles. This is the first study to show the presence of PCBs in xylem sap (range: 0.03-0.18 μg·mL(-1)), confirming that PCB translocation throughout the plant occurs via this medium. A comparison of soil (5.2 ± 2.5 μg·g(-1)), root (27.1 ± 2.1 μg·g(-1)), shoot (range: 1.9 ± 0.5 μg·g(-1) - 8.2 ± 1.4 μg·g(-1)), and xylem sap (0.09 ± 0.04 μg·g(-1)) samples showed significant differences in congener profiles, with lower chlorinated congeners (predominately trichlorinated ones) found within xylem sap in higher amounts than higher chlorinated congeners. The total PCB concentrations of xylem sap samples collected at various lengths along the primary plant shoot were not significantly different from each other, while those of primary shoot tissue samples significantly decreased (two-sample t test, p = 0.01) as the distance from the plant base increased. PCA analysis of individual congeners in the roots, shoots and xylem sap indicated that movement of the PCB congeners in the plant was affected by the number of chlorines in the molecule, and hence possibly log K(ow) and molecular weight, but not by planarity.

Effect of plant age on PCB accumulation by Cucurbita pepo ssp. pepo.

A greenhouse experiment was conducted to investigate polychlorinated biphenyl (PCB) uptake and translocation from soil over time in pumpkin plants (Cucurbita pepo ssp. pepo cv. Howden). Plants were grown in weathered soil collected from a former industrial site contaminated with Aroclor 1248 (mean [PCB](soil) = 6.5 mg kg(-1)). Plants were harvested five times over 42 d and analyzed for total PCB concentration in the root and shoot tissues. The concentration of PCBs in the root was not significantly different between harvests (mean [PCB](root) = 21.5 mg kg(-1)). The concentration of PCBs in the shoots was also relatively stable over time (mean [PCB](shoot) = 3.5 mg kg(-1)) despite increases in shoot biomass (fresh weight of 4.3 g at Day 12 to 59 g at Day 42). This suggests that PCBs were continuously accumulated throughout the growth period. The trends found in this study indicate the optimal time to harvest C. pepo ssp pepo plants to maximize PCB phytoextraction is when the plant shoot has reached its maximum biomass.

Transplacental benzene exposure increases tumor incidence in mouse offspring: possible role of fetal benzene metabolism

Childhood cancer is the leading cause of disease-related death in children aged 1-14 years in Canada and the USA and it has been hypothesized that transplacental exposure to environmental carcinogens such as benzene may contribute to the etiology of these cancers. Our objectives were to determine if transplacental benzene exposure increased tumor incidence in mouse offspring and assess fetal benzene metabolism capability. Pregnant CD-1 and C57Bl/6N mice were given intraperitoneal injections of corn oil, 200 mg/kg, or 400 mg/kg benzene on gestational days 8, 10, 12 and 14. A significant increase in tumor incidence was observed in CD-1, but not C57BL/6N, 1-year-old offspring exposed transplacentally to 200 mg/kg benzene. Hepatic and hematopoietic tumors were predominantly observed in male and female CD-1 offspring, respectively. Female CD-1 offspring exposed transplacentally to 200 mg/kg benzene had significantly suppressed bone marrow CD11b(+) cells 1 year after birth, correlating with reduced colony-forming unit granulocyte/macrophage numbers in 2-day-old pups. CD-1 and C57Bl/6N maternal blood benzene levels and fetal liver benzene, t, t-muconic acid, hydroquinone and catechol levels were analyzed by gas chromatography/mass spectrometry. Significant strain-, gender- and dose-related differences were observed. Male CD-1 fetuses had high hydroquinone levels, whereas females had high catechol levels after maternal exposure to 200 mg/kg benzene. This is the first demonstration that transplacental benzene exposure can induce hepatic and hematopoietic tumors in mice, which may be dependent on fetal benzene metabolism capability.