Patricia Abad-Valle

Arsenic distribution in soils and rye plants of a cropland located in an abandoned mining area.

A mining impacted cropland was studied in order to assess its As pollution level and the derived environmental and health risks. Profile soil samples (0-50 cm) and rye plant samples were collected at different distances (0-150 m) from the near mine dump and analyzed for their As content and distribution. These cropland soils were sandy, acidic and poor in organic matter and Fe/Al oxides. The soil total As concentrations (38-177 mg kg(-1)) and, especially, the soil soluble As concentrations (0.48-4.1 mg kg(-1)) importantly exceeded their safe limits for agricultural use of soils. Moreover, the soil As contents more prone to be mobilized could rise up to 25-69% of total As levels as determined using (NH4)2SO4, NH4H2PO4 and (NH4)2C2O4·H2O as sequential extractants. Arsenic in rye plants was primarily distributed in roots (3.4-18.8 mg kg(-1)), with restricted translocation to shoots (TF=0.05-0.26) and grains (TF=<0.02-0.14). The mechanism for this excluder behavior should be likely related to arsenate reduction to arsenite in roots, followed by its complexation with thiols, as suggested by the high arsenite level in rye roots (up to 95% of the total As content) and the negative correlation between thiol concentrations in rye roots and As concentrations in rye shoots (|R|=0.770; p<0.01). Accordingly, in spite of the high mobile and mobilizable As contents in soils, As concentrations in rye above-ground tissues comply with the European regulation on undesirable substances in animal feed. Likewise, rye grain As concentrations were below its maximum tolerable concentration in cereals established by international legislation.

Evaluation of the Variables that Influence Mercury Capture in Solid Sorbents

Fly ashes are by-products generated during coal combustion in power plants. These byproducts are able to capture volatile species, such as mercury that are evaporated from coal in different proportions. The precise mechanism by which a trace element is retained in the fly ashes is not fully understood. The quantity of mercury retained may vary from fly ash to fly ash and depends on the process conditions. It has been observed that, although some fly ash inorganic components exhibit a low capacity for mercury retention, the unburned material in the fly ash may benefit its adsorption. There are a number of variables that may influence mercury retention by fly ash components and the exact nature of Hg-fly ash interactions needs to be investigated more thoroughly. The aim of the present work was to evaluate the variables that have an effect on the retention of Hg and HgCl2 in fly ashes originated by burning coals of different rank and nature. The mercury retention capacity of these fly ashes was compared with retention in commercial activated carbons in coal combustion and inert atmospheres. The study was carried out in a laboratory scale reactor using the sorbent as a fixed bed. The amount of mercury retained was determined by analyzing the sorbents post-retention by means of cold vapor atomic absorption (CV-AA). The results obtained indicate that the quantity of mercury captured depends on the characteristics of the fly ashes and on the mode of occurrence of mercury in gas phase. The retention of mercury in the fly ashes studied is greatly influenced by the gas composition. It was inferred that, unlike the activated carbons, the fly ashes show different retention capacities and efficiencies for mercury in combustion and inert atmospheres. Moreover, mercury retention may be modified by variations in the unburned coal particle content

Arsenic distribution in a pasture area impacted by past mining activities

Former mine exploitations entail a serious threat to surrounding ecosystems as after closure of mining activities their unmanaged wastes can be a continuous source of toxic trace elements. Quite often these mine sites are found within agricultural farming areas, involving serious hazards as regards product (feed/food) quality. In this work a grazing land impacted by the abandoned mine exploitation of an arsenical deposit was studied so as to evaluate the fate of arsenic (As) and other trace elements and the potential risks involved. With this aim, profile soil samples (0-50cm) and pasture plant species (Agrostis truncatula, Holcus annus and Leontodon longirostris) were collected at different distances (0-100m) from the mine waste dump and analyzed for their trace element content and distribution. Likewise, plant trace element accumulation from impacted grazing soils and plant trace element translocation were assessed. The exposure of livestock grazing animals to As was also evaluated, establishing its acceptability regarding food safety and animal health. International soil guideline values for As in grazing land soils (50mgkg-1) resulted greatly exceeded (up to about 20-fold) in the studied mining-affected soils. Moreover, As showed a high mobilization potential under circumstances such as phosphate application or establishment of reducing conditions. Arsenic exhibited relatively high translocation factor (TF) values (up to 0.32-0.89) in pasture plant species, reaching unsafe concentrations in their above-ground tissues (up to 32.9, 16.9 and 9.0mgkg-1 in Agrostis truncatula, Leontodon longirostris and Holcus annus, respectively). Such concentrations represent an elevated risk of As transfer to the high trophic-chain levels as established by international legislation. The limited fraction of arsenite found in plant roots should play an important role in the relatively high As root-to-shoot translocation shown by these plant species. Both soil ingestion and pasture intake resulted important entrance pathways of As into livestock animals, showing quite close contribution levels. The cow acceptable daily intake (ADI) of As regarding food safety was surpassed in some locations of the study area when the species Agrostis truncatula was considered as the only pasture feed. Restrictions in the grazing use of lands with considerable As contents where this plant was the predominant pasture species should be established in order to preserve food quality. Therefore, the exposure of livestock animals to As via both soil ingestion and pasture consumption should be taken into account to establish the suitability of mining-impacted areas for gazing.

Trace element levels in an area impacted by old mining operations and their relationship with beehive products

The environmental status of an area impacted by Roman mining activities was assessed in order to establish the current risks posed by such old mine emplacements. For this purpose, soil samples were collected throughout the mining area and analysed for their total, mobile and mobilizable trace element (As, Cd, Mo, Sb and Zn) contents. Additionally, beehive products (honey and pollen) were also sampled and evaluated for their use as environmental indicators of the area. The results obtained were compared with those from a control non-polluted area. The mine soils presented slightly increased levels of Cd and Sb (about 2- to -3-fold their normal soil concentrations), whereas the enrichment of As reached considerable levels, with concentrations almost ten-fold of those considered the threshold for causing toxicity. Leachable As contents exhibited very high values (1.2-21.9mgkg-1), indicating the need for risk attenuation measures. All trace elements were mainly partitioned in the soil residual fraction, especially Mo (76-99%) and Sb (61-91%). Significant partitioning levels were also found in the reducible fraction of As (up to 35%) and Cd (up to 38%), and in the oxidizable fraction of Mo (up to 23%). The reducible pool of As was particularly relevant due to the eventual mobilization of this element under reducing conditions. Among the beehive products tested, honey proved not to be useful as an environmental indicator, whereas pollen showed great potential as an indicator when the contamination levels were moderate to high.