title: Soil acidification as a confounding factor on metal phytotoxicity in soils spiked with copper-rich mine wastes.
abstract: Pollution of soil with mine wastes results in both Cu enrichment and soil acidification. This confounding effect may be very important in terms of phytotoxicity, because pH is a key parameter influencing Cu solubility in soil solution. Laboratory toxicity tests were used to assess the effect of acidification by acidic mine wastes on Cu solubility and on root elongation of barley (Hordeum vulgare L.). Three contrasting substrates (two soils and a commercial sand) and two acidic, Cu-rich mine wastes (oxidized tailings [OxT] and smelter dust [SmD]) were selected as experimental materials. Substrates were spiked with a fixed amount of either SmD or OxT, and the pH of experimental mixtures was then modified in the range of 4.0 to 6.0 and 7.0 using PIPES (piperazine-1,4-bis(2-ethanesulfonic acid)), MES (2-(N-morpholino)ethanesulfonic acid), and MOPS (3-(N-Morpholino)-propanesulfonic acid) buffers. Chemical (pore-water Cu and pH) and toxicological (root length of barley plants) parameters were determined for experimental mixtures. Addition of SmD and OxT to substrates resulted in acidification (0.11-1.16 pH units) and high levels of soluble Cu and Zn. Neutralization of experimental mixtures with MES (pH 6.0) and MOPS (pH 7.0) buffers resulted in a marked decrease in soluble Cu and Zn, but the intensity of the effect was substrate-dependent. Adjustment of soil pH above the range normally considered to be toxic to plants (pH in water extract, > 5.5) significantly reduced metal toxicity in barley, but phytotoxicity was not completely eliminated. The present results stress the importance of considering confounding effects on derivation of toxicity thresholds to plants when using laboratory phytotoxicity tests.
authors.affiliation: Centro de Investigación Minera y Metalúrgica, Av. Parque Antonio Rabat 6500, Vitacura, Santiago, Chile. rginocc@cimm.cl
authors.forename: Rosanna
authors.initials: R
authors.lastname: Ginocchio
authors.forename: Luz María
authors.initials: LM
authors.lastname: De la Fuente
authors.forename: Pablo
authors.initials: P
authors.lastname: Sánchez
authors.forename: Elena
authors.initials: E
authors.lastname: Bustamante
authors.forename: Yasna
authors.initials: Y
authors.lastname: Silva
authors.forename: Paola
authors.initials: P
authors.lastname: Urrestarazu
authors.forename: Patricio H
authors.initials: PH
authors.lastname: Rodríguez
mesh_terms: D015986:Confounding Factors, Epidemiologic; D003300:Copper / Q000032:analysis* / Q000633:toxicity*; D001467:Hordeum; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste / Q000009:adverse effects / Q000032:analysis*; D008906:Mining; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development; D012987:Soil / Q000032:analysis*; D012989:Soil Pollutants / Q000032:analysis* / Q000633:toxicity; D012995:Solubility; D018675:Toxicity Tests
chemical_list: D007220:Industrial Waste; D012987:Soil; D012989:Soil Pollutants; D003300:Copper