Growth conditions impact 2,2-bis (p-chlorophenyl)-1,1-dichloroethylene (p,p′-DDE) accumulation byCucurbita pepo

Abstract

Laboratory experiments were conducted to study the effects of soil moisture content, planting density, plant age, and the growth of multiple generations on the bioconcentration of weathered p,p'-DDE by the plant Cucurbita pepo. As soil moisture content increased from 7.4% to 29.9% (by weight), rates of contaminant accumulation by plant roots were increased by more than a factor of 2. Higher planting density also led to higher uptake, as the root bioconcentration factor (BCF, dry-weight ratio of contaminant concentration in the tissue to that in the soil) increased by 15-fold as the number of plants per pot was raised from 1 to 3. Concentrations of the compound in plant roots were inversely related to plant age, with root BCF declining by approximately a factor of 3 as plants aged from 14 to 28 d. Finally, no change in the bioavailability of the compound was observed in successive generations of plants grown in the same contaminated soil. The results suggest that phytoremediation is influenced by a number of factors and that the cleanup of contaminated soil can be enhanced by an understanding of environmental and other conditions affecting plant growth and bioconcentration.

Effect of Plant Age on PCB Accumulation by Cucurbita pepo ssp. pepo

“…There was also no significant difference between the PCB concentration in the initial field soil (mean 6.5 ± 0.95 mg kg −1 ) and the soil concentration following any of the harvests (ANOVA of log e – transformed soil [PCB], F 0.05,5,37 = 0.179, p = 0.969). This result is not unexpected, as significant decreases in soil POPs concentration due to phytoextraction have previously only been observed for p,p ′‐DDE after two (White et al, 2003b) or three (Kelsey et al, 2006) plantings and both of these studies used p,p′ ‐DDE at an order of magnitude lower concentration.…”

“…pepo plants demonstrate their PCB-accumulating proper-ties best in uncrowded fi eld conditions as compared to crowded greenhouse conditions (Whitfi eld Åslund et al, 2008). Th us the diff erence in concentration over time between the fi ndings of the present study and the Kelsey et al (2006) study may be related to container size which aff ects planting density.…”

“…Kelsey et al (2006) observed the p,p ′‐DDE concentration in roots, stems, and leaves of C. pepo ssp. pepo plants was highest after 14 d of growth and then decreased in harvests at 21 and 28 d. This study used small pots containing 500 g of soil, in comparison to the current study with much larger containers filled with more than 7000 g of contaminated soil.…”

“…Most of these studies have only considered the concentration of contaminant in the tissue at the end of the growing season, while the concentration of the contaminant through the growth period remains unknown (An et al, 2006; Inui et al, 2008; Pendergrass and Butcher, 2006; Wang et al, 2004; White et al, 2003a). Uptake over time has been investigated for p,p ′‐DDE but results were mixed regarding concentration trends in various tissues (Kelsey et al, 2006; White et al, 2006). There are no published studies investigating PCB uptake over time and this information is critical for optimizing PCB phytoextraction.…”

Effect of pumpkin root exudates on ex situ polychlorinated biphenyl (PCB) phytoextraction by pumpkin and weed species

“…Despite this difference, it is unlikely that it was caused by plant uptake of PCBs, as only ∼0.6% of the total PCBs were extracted from the soil by each of the two groups. Previous phytoextraction studies of various POPs have shown that a decrease in soil concentration is generally only observed after multiple plantings (Kelsey et al 2006;Lunney et al 2004;Zeeb et al 2006). Contaminant heterogeneity is often a confounding factor when working with historically contaminated and naturally weathered industrial soil, despite significant homogenization efforts prior to experimentation.…”