Introduction:

There is currently a growing demand for hydrocarbons, which has led to the use of non-dynamic technologies, such as hydraulic fracturing. However, this technique causes environmental damages to ecosystems due to the generation of sewage sludge such as the thorny Tamaulipas scrubland that is located within the Burgos basin, an area of economic relevance for conventional gas exploitation. The objective of the study was to evaluate the germination of Acacia farnesiana (L.) Willd and Ebenopsis ebano (Berl.) Barneby and its potential use with biostimulation in the removal of As, Cd and Zn in sewage sludge from the extraction of shale gas.

Method:

Seeds of Acacia farnesiana (L.) Willd and Ebenopsis ebano (Berl.) Barneby were collected in the ejido El Zaus, municipality of Hidalgo, Tamaulipas. The germination index (GI) was evaluated according to Zucconi. Twenty-three treatments were set by considering the substrates (two types of slugde, soil and a mixture of both substrates), the two species of seedlings (Acacia and Ebenopsis), and the biostimulation with a 46% urea solution. Pots of 3 kg were used as experimental units, in where three seedlings were planted with three replicates per treatment. A final sampling of each treatment was performed for the corresponding determinations of As, Cd, Zn, P and K, which were carried out by extraction of DTPA, and subsequently carried out by plasma induction atomic emission spectroscopy (ICP-OES Varian model 725-ES, Agilent Mulgrave, Australia). The total nitrogen (Nt) in seedlings and substrates, was carried out using the micro Kjeldahl method, and organic matter (OM) content was estimated by Walkely Black method.

Results:

Differences in IG were observed (P = 0.02374). Results indicated that the structural (size) and physiological (embryo viability) characteristics of the seeds are related to the germination capacity of both species under contaminated substrates. Significant differences were found in the concentrations of As, Cd, and Zn, through treatment (P <0.0001). The accumulation of As, Cd and Zn, was determined by the structure of the plant (root > stem > leaf).

Conclusion:

Germination index of Acacia farnesiana (L.) Willd and Ebenopsis ebano (Berl.) Barneby in aqueous substrates of residual sludge is based on structural and physiological characteristics of each species. Removal of As, Cd and Zn, was influenced by the species, the substrate, the urea biostimulation, and the presence of OM, which confer the plug effect that controls the alkalinity of the substrates and therefore, the mobility of the metals.

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