Substrate evaluation for biobeds in the degradation of ethylene bis-dithiocarbamate in wastewater from pesticide application in banana.

The efficacy of biobeds was evaluated by testing three agricultural residues (sugarcane top, banana stem, and eucalyptus chip) as substrates for the degradation of ethylene bis-dithiocarbamate (EBDC) and ethylene thiourea (ETU) in wastewater from banana spraying. Acrylic columns with a capacity to treat 1 L/ea. of wastewater were used as experimental units. Each unit was filled with different proportions of the test substrate (30%, 50% and 70% v/v) and the difference in volume was made up of equal parts of sugar cane cachasse and Fluvisol soil. Subsequently, the units were contaminated with suspensions of 878 mgL-1 of EBDC, and the dose was repeated periodically. The ETU concentration and leachate toxicity were evaluated every month for six months. The mixtures with 30% sugarcane top and 50% eucalyptus chip gave the best results, with leachable ETU concentrations down to a level protective of the environment, and toxicity down to background levels or nearly so. This was only found in mixtures with a high C:N ratio (20-25), thus, the effectiveness of the biobeds appears to be related to high lignolytic activity. .

Human health risks from fish consumption following a catastrophic gas oil spill in the Chiquito River, Veracruz, Mexico.

An industrial accident resulted in a gas oil spill of 11,808 barrels in the upper part of the Coatzacoalcos River watershed. After river shore cleanup, concentrations of total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAH) in muscle (+ skin) were determined in captured fish to evaluate human health risk due to fish consumption post-spill in the most affected communities. Data on fish consumption, body weight, and diet factor were collected by questionnaires and field observations. Using standard formulas for carcinogenic and non-carcinogenic substances, site-specific remediation levels were calculated in fish, comparing them to the real levels observed. Likewise, the levels of PAHs in fish captured pre- and post-spill were compared to determine their origin (pyrolytic vs. petrogenic). The TPH concentrations were between 119,000 and 523,000 ng/g (dry weight) and no significant difference (P > 0.05) was found pre- vs. post-spill. The concentration of total PAHs varied between 2494.83 and 35,412.23 ng/g (dry weight), with the concentrations of naphthalene (520.9 ng/g) and phenanthrene (7532.7 ng/g) being much higher than in control samples, and being from the gas oil spill (petrogenic origin). The site-specific remediation levels calculated for TPH and PAH were much higher than the maximum levels actually detected. No human health risks were found from hydrocarbons from the spill, at least after cleanup efforts and natural attenuation (six months).

Soil Odor as An Extra-Official Criterion for Qualifying Remediation Projects of Crude Oil-Contaminated Soil.

Unfortunately, many property owners in southeastern Mexico do not trust environmental authorities, and the de facto method they use to evaluate the progress in environmental remediation projects is soil smell. This criterion was evaluated to determine if it was reliable to assess soil fertility and toxicity. Three soils (Fluvisol, Gleysol, and Arenosol), were contaminated with 2% medium or heavy crude oil (30.2, 17.1°API, respectively), and treated for 18 months to simulate bioremediation or natural attenuation. Every two months, field capacity, water repellency, hydrocarbon concentration, acute toxicity and soil odor were measured. Odor was measured in controlled conditions with a group of unexperienced panelists. During remediation, the Fluvisol and Gleysol were perceived to have an odor intensity between slight to low, and were considered acceptable. Meanwhile, in the Arenosol, the odor intensity was between low to medium and was considered unacceptable. After treatment, the hydrocarbon concentration was reduced to low levels, very near Mexican norm, and all the soils, including the Arenosol, were perceived to have an intensity between neutral to slightly agreeable, were considered acceptable, and no toxicity was observed in the earthworm bioassay (no false positives). However, in various soil samples from the Fluvisol and Arenosol, important risks were present with respect to field capacity and water repellency. Due to these observations, even though soil smell may be a trustworthy guide to soil toxicity, it does not ensure that the remediated soil's fertility has been restored.

Fertility Deterioration in a Remediated Petroleum-Contaminated Soil.

A soil that had been remediated by soil washing and chemical oxidation was evaluated, comparing it to an uncontaminated control soil ~30 m away. Profile descriptions were made of both soils over a 0-1 m depth, and samples were analyzed from each soil horizon. Samples were also analyzed from surface soil (0-30 cm). The control soil (a Fluvisol), had several unaltered A and C horizons, but the remediated soil presented only two poorly differentiated horizons, without structure and much lower in organic matter (<0.5%). In surface samples (0-30 cm), the bulk density, sand-silt-clay contents, field capacity, organic matter, and porosity were different with respect to the control (p > 0.05), and there was much greater compaction (3.04 vs. 1.10 MPa). However, the hydrocarbon concentration in the remediated soil was low (969.12 mg kg-1, average), and was not correlated to soil fertility parameters, such as porosity, organic matter, pH, moisture, field capacity or texture (R2 < 0.69), indicating that the impacts (such as compaction, lower field capacity and moisture content) were not due to residual hydrocarbons. Likewise, acute toxicity (Microtox) was not found, nor water repellency (penetration time < 5 s). It was concluded that the fertility deterioration in this soil was caused principally from the mixture of upper (loam) and lower (silty clay to silty clay loam) horizons during remediation treatment. Another important factor was the reduction in organic material, probably caused by the chemical oxidation treatment.