Three year field test of a plant growth promoting rhizobacteria enhanced phytoremediation system at a land farm for treatment of hydrocarbon waste.

Phytoremediation of total petroleum hydrocarbons (TPH) has the potential to be a sustainable waste management technology if it can be proven to be effective in the field. Over the past decade, our laboratory has developed a system which utilizes plant growth promoting rhizobacteria (PGPR) enhanced phytoremediation (PEP) that, following extensive greenhouse testing, was shown to be effective at remediating TPH from soils. This system consists of physical soil manipulation and plant growth following seed inoculation with PGPR. PGPR elicit biomass increases, particularly in roots, by minimizing plant stress in highly contaminated soils. Extensive development of the root system enhances degradation of contaminants by the plants and supports an active rhizosphere that effectively promotes TPH degradation by a broad microbial consortium. Following promising greenhouse trials, field tests of PEP were performed over a period of three years at a Southern Ontario site (approximately 130 g kg(-1) TPH) used for land farming of refinery hydrocarbon waste for many years. The low molecular weight fractions (the Canadian Council of Ministers of the Environment (CCME) fractions 1 and 2) were removed through land farming and bioremediation; the high molecular weight, recalcitrant fractions (CCME fractions 3 and 4) remained at high levels in the soil. Using PEP, we substantially remediated fractions 3 and 4, and lowered TPH from 130 g kg(-1) to approximately 50 g kg(-1) over a three year period. The amount of plant growth and extent of oil remediation were consistently enhanced by PGPR.

A predictive quantitative structure-activity relationship model for the photoinduced toxicity of polycyclic aromatic hydrocarbons to Daphnia magna with the use of factors for photosensitization and photomodification.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that readily absorb environmentally relevant solar ultraviolet radiation. On absorption of a photon, photoinduced toxicity of PAHs is manifested through photosensitization and photomodification. Both of these processes occur under environmentally relevant levels of actinic radiation. An empirical quantitative structure-activity relationship model previously developed was explanatory of photoinduced toxicity of 16 PAHs in Lemna gibba (duckweed). This model was found to be predictive of toxicity to Vibrio fischeri. The L. gibba quantitative structure-activity relationship showed that a photosensitization factor and a photomodification factor could be combined to describe photoinduced toxicity. To further examine this model, we assessed whether it could be applied to Daphnia magna (water flea), a key bioindicator species in aquatic ecosystems. Toxicity was assessed as median effective concentration and median effective time for immobility. As with L. gibba and V. fischeri, neither the photosensitization factor nor the photomodification factor alone correlated to toxicity in D. magna. However, a photosensitization factor modified for D. magna exhibited a correlation to toxicity (r2 = 0.86), which was modestly improved when summed with a modified photomodification factor (r2 = 0.92). The greatest correlation was observed with median effective concentration data. This research provides evidence that models incorporating factors for photosensitization and photomodification have interspecies applicability.

Photoinduced toxicity of polycyclic aromatic hydrocarbons to Daphnia magna: ultraviolet-mediated effects and the toxicity of polycyclic aromatic hydrocarbon photoproducts.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants known for their photoinduced toxicity. This toxicity may occur through two mechanisms: Photosensitization, and photomodification. Photosensitization generally leads to the production of singlet oxygen, a reactive oxygen species that is highly damaging to biological molecules. Photomodification of PAHs, usually via oxidation, results in the formation of new compounds and can occur under environmentally relevant levels of actinic radiation. The toxicities of 16 intact PAHs to Daphnia magna were assessed under two ultraviolet radiation conditions. The toxicity of intact PAHs generally increased in the presence of full-spectrum simulated solar radiation relative to that in the presence of visible light plus ultraviolet A only. Despite the knowledge of a bipartite mechanism of phototoxicity that includes photosensitization and photomodification, few studies have examined the effects of PAH photoproducts on animals. To expand the existing data, 14 PAH photoproducts (oxy-PAHs) also were assayed, most of which were highly toxic without further photomodification. Two photoproducts of benzo[a]pyrene, 1,6- and 3,6-benzo[a]pyrenequinone, were the most toxic compounds tested, followed closely by benz[a]anthraquinone. Each of these three compounds had a median effective concentration in the low nanomolar range. The data presented highlight the effects of ultraviolet radiation on mediating PAH toxicity and the need to analyze absorption spectra of contaminants in the prediction of photoinduced toxicity. The importance of the role of photomodification also is stressed, because several oxy-PAHs, an unregulated group of contaminants, were highly toxic to D. magna, a key bioindicator species in aquatic ecosystems.