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Arsenic distribution in mesquite (Prosopis laevigata) and huizache (Acacia farnesiana) in the Zimapán mining area, México

¹ Universidad Nacional Autonoma de Mexico, Instituto de Geofisica, UNAM, C.U., México 04510, D.F. Mexico(victoria{at}geofisica.unam.mx)
² Unity College, 90 Quaker Hill Rd., Unity, ME 04988, USA (longley{at}unity.edu)
³ Department of Natural Sciences, Castleton State College, Castleton, VT 05735 USA (Helen.Mango{at}castleton.edu)
⁴ Instituto de Geologia, UNAM, Circuito Exterior, C.U., México 04510, D.F. Mexico (mgvc{at}servidor.unam.mx)

Arsenic concentrations have been determined in mesquite (Prosopis laevigata) and huizache (Acacia farnesiana) growing on As-rich soils in the semi-arid mining area of Zimapán, México. The elevated As contents in the substrates (up to 32 000 mg/kg) were reflected in the dry weight concentrations of twigs (up to 82.7 mg/kg in mesquite and 225 mg/kg in huizache), and leaves (up to 78.2 mg/kg in mesquite and 67.0 mg/kg in huizache). Arsenic concentrations in twigs and leaves collected in less impacted soils (containing up to 110 mg/kg of As) reached a maximum of 20.8 mg/kg in mesquite twigs and 27.8 mg/kg in mesquite leaves. Differences of several orders of magnitude in surface substrate As concentrations were not reflected in plant As contents. A low proportion of available As in substrates, as well as deep plant roots which may reach less contaminated sediments, explains this behaviour. The pod As concentrations from tailings-affected sites were not significantly different from background samples. Nearly all mesquites and huizaches from the high-As substrates were above standards for foodstuffs. The As concentration in vegetation growing on soils affected by tailings and smelter/slags points to a potential contamination of the food chain, mainly through goats, the most common mammals in the area. Mesquites and huizaches are not hyperaccumulators but are As-tolerant plants and can therefore be considered as an option for a remediation programme to stabilize eroding tailings.

KEYWORDS: biogeochemistry, arsenic, mining, plants, Zimapán, México