Updating risk remediation-endpoints for petroleum-contaminated soils? a case study in the Ecuadorian Amazon region

In Ecuador, the regulatory framework for the remediation of petroleum-contaminated soils is based on predefined concentration endpoints for a selected range of petroleum hydrocarbon compounds. However, such approach may lead to over or under-estimation of the environmental risk posed by contaminated soils. In this study, the end-point remediation criteria according to Ecuadorian Environmental legislation were evaluated using different approaches. The first one was based on Total Extractable Petroleum Hydrocarbons (TEPH) and the second one on Total Bioavailable Petroleum Hydrocarbons (TBPH). Both were compared with ecotoxicological determinations using EC50 -Microtox® bioassay at 5 and 15 min of exposure. The correlation (R2) between EC50 values vs TEPH was of 0.2 and 0.25 for 5 and 15 min, respectively. Meanwhile, R2 between EC50 and TBPH was of 0.9 and 0.65 for 5 and 15 min, respectively, demonstrating a stronger correlation. Our results suggest that a contaminated site where the concentration of the TEPH is higher than the relevant regulatory concentrations may be deemed to present an acceptable risk even though their concentrations exceed the target values in soils. The results also challenge the notion that hormesis is associated with TEPH, contrary to some literature. This study is the first in Ecuador to propose incorporating bioavailability into environmental regulations, highlighting the need for further research to establish realistic and achievable remediation goals based on toxicity studies involving various trophic levels

Estudio isotérmico de remoción de cromo (VI) en solución acuosa empleando perlas de alginato con Chlorella sp. inmovilizada.

The objective of the present investigation was to study the removal of chromium (VI) in aqueous solution by means of isothermal models using alginate beads with Chlorella sp. immobilized and alginate beads without Chlorella sp.; the removal was evaluated using solutions of chromium at different concentrations. To determine the kinetics of removal, samples of aqueous solution were obtained in a range of 0-240 minutes. Then, the removal of the metal at pH 4 and 5 and at different cell densities of Chlorella sp. (0.3x107; 1.6x107; 3x107 cells/mL of alginate). Finally, the effect of the initial concentration of chromium was evaluated, analyzing six concentrations (0-20 mg/L). All the tests were analyzed by Atomic Absorption spectrometer, obtaining the highest percentage of removal at a contact time of 224 min, pH 5 and 3x107 cells/mL with 81.09% and 72.20% removal by the action of the alginate beads with Chlorella sp. and alginate beads without Chlorella sp, respectively. Three isothermal models were analyzed, the Langmuir isotherm being the one that was best adjusted to describe the adsorption process, determining a maximum adsorption capacity of 5.08 mg/g for alginate beads with Chlorella sp. and 3.74 mg/g for the alginate beads without Chlorella sp, concluding that there is a greater adsorption capacity when immobilizing Chlorella sp. in pearls of alginate. In addition, the isothermal analysis allows to recommend its possible use in the treatment of water contaminated with chromium (VI).La presente investigación tuvo como objetivo estudiar la remoción de cromo (VI) en solución acuosa mediante modelos isotérmicos empleando perlas de alginato de calcio con Chlorella sp. inmovilizada y perlas de alginato de calcio sin Chlorella sp.; la remoción se evaluó utilizando soluciones de cromo a diferentes concentraciones. Para determinar la cinética de remoción se obtuvieron muestras de solución acuosa en un intervalo de 0-240 minutos. Luego, se evaluó la remoción del metal a pH 4 y 5 y a diferentes densidades celulares de Chlorella sp. (0.3x107; 1.6x107; 3x107 células/mL de alginato). Por último, se evaluó el efecto de la concentración inicial de cromo, analizando seis concentraciones (0-20 mg/L). Todos los ensayos se analizaron mediante espectrometría de Absorción Atómica, obteniendo el mayor porcentaje de remoción a un tiempo de contacto de 224 min, pH 5 y 3x107 células/mL con 81.09% y 72.20% de remoción por acción de las perlas de alginato con Chlorella sp. y perlas de alginato sin Chlorella sp, respectivamente. Se analizaron tres modelos isotérmicos siendo la isoterma de Langmuir aquella que se ajustó de mejor manera para describir el proceso de adsorción, determinando una capacidad máxima de adsorción de 5.08 mg de Cr/g para las perlas de alginato con Chlorella sp. y 3.74 mg/g para las perlas de alginato sin Chlorella sp, concluyendo que existe una mayor capacidad de adsorción al inmovilizar Chlorella sp. en perlas de alginato. Además, el análisis isotérmico permite recomendar su posible uso en el tratamiento de aguas contaminadas con cromo (VI)