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Highlights • Recalcitrant fractions of petroleum hydrocarbon (TPH) cometabolized for remediation • Biostimulation provides propitious environment for degraders in the rhizosphere • Bioaugmentation can supplement the catabolic activities of rhizosphere communities • Effective rhizoremediation requires the modulation of plant-microbial associations • Rhizoremediation of TPH-contaminated sites is a risk-based phytomanagement strategy

Microplastics (MPs) exposed to the natural environment provide an ideal surface for biofilm formation, which potentially acts as a reactive phase facilitating the sorption of hazardous contaminants. Until now, changes in the contaminant sorption capacity of MPs due to biofilm formation have not been quantified. This is the first study that compared the capacity of naturally aged, biofilm-covered microplastic fibers (BMFs) to adsorb perfluorooctane sulfonate (PFOS) and lead (Pb) at environmentally relevant concentrations. Changes in the surface properties and morphology of aged microplastic fibers (MF) were studied by surface area analysis, infrared spectroscopy, and scanning electron microscopy. Results revealed that aged MFs exhibited higher surface areas because of biomass accumulation compared to virgin samples and followed the order polypropylene>polyethylene>nylon>polyester. The concentrations of adsorbed Pb and PFOS were 4–25% and 20–85% higher in aged MFs and varied among the polymer types. The increased contaminant adsorption was linked with the altered surface area and the hydrophobic/hydrophilic characteristics of the samples. Overall, the present study demonstrates that biofilms play a decisive role in contaminant-plastic interactions and significantly enhance the vector potential of MFs for toxic environmental contaminants. We anticipate that knowledge generated from this study will help refine the planetary risk assessment of MPs.

This study explores interactions between As and Fe­(III) minerals, predominantly schwertmannite and jarosite, in acid mine drainage (AMD) via observations at a former mine site combined with mineral formation and transformation experiments. Our objectives were to examine the effect of As on Fe­(III) mineralogy in strongly acidic AMD while also considering associated controls on As mobility. AMD at the former mine site was strongly acidic (pH 2.4 to 2.8), with total aqueous Fe and As decreasing down the flow-path from ∼400 to ∼20 mg L–1 and ∼33,000 to ∼150 μg L–1, respectively. This trend was interrupted by a sharp rise in aqueous As­(III) and Fe­(II) caused by reductive dissolution of As-bearing Fe­(III) phases in a sediment retention pond. Attenuation of Fe and As mobility occurred via formation of As­(V)-rich schwertmannite, As­(V)-rich jarosite, and amorphous ferric arsenate (AFA), resulting in solid-phase As concentrations spanning ∼13 to ∼208 g kg–1. Schwertmannite and jarosite retained As­(V) predominantly by structural incorporation involving AsO4-for-SO4 substitution at up to ∼40 and ∼22 mol %, respectively. Arsenic strongly influenced Fe­(III) mineral formation, with high As­(V) concentrations causing formation of AFA over schwertmannite. Arsenic also strongly influenced Fe­(III) mineral evolution over time. In particular, increasing levels of As­(V) incorporation within schwertmannite were shown, for the first time, to enhance the transformation of schwertmannite to jarosite. This significant discovery necessitates a re-evaluation of the prevailing paradigm that As­(V) retards schwertmannite transformation.

Barium (Ba) is a nonessential element to terrestrial organisms and is known to be toxic at elevated concentrations. In this study, the bioavailability and toxicity of Ba in barite (BaSO4) contaminated soils was studied using standard test organisms (Lactuca sativa L. "Great Lakes", Eisenia fetida). Contamination resulted from barite mining activities. Barium concentrations in contaminated soils determined by X-ray fluorescence were in the range 0.13-29.2%. Barite contaminated soils were shown to negatively impact both E. fetida and L. sativa relative to control soil. For E. fetida, pore-water concentrations and acid extractable Ba were linearly related to % body weight loss. In L. sativa, pore-water Ba and exchangeable Ba were both strongly related to shoot Ba and shoot biomass production. A negative linear relationship was observed between shoot Ba content and shoot weight (P < 0.0004, R(2) = 0.39), indicating that Ba accumulation is likely to have induced phytotoxicity. Plant weights were correlated to % weight loss in earthworm (r = -0.568, P = 0.028). Barium concentrations in pore-water were lower than predicted from barite solubility estimates but strongly related to exchangeable Ba, indicating an influence of ion exchange on Ba solubility and toxicity to E. fetida and L. sativa.