Maria Dolores Mingorance

Persistence of two neonicotinoid insecticides in wastewater, and in aqueous solutions of surfactants and dissolved organic matter.

Wastewater treatment plants receive organic contaminants, such as pesticides, which reach the sewage system from domestic, industrial or agricultural activities. In wastewater, which is a complex mixture of organic and inorganic compounds, biotic or abiotic degradation of contaminants can be affected by the presence of co-solutes. The photodecomposition in natural sunlight of two neonicotinoid insecticides, thiamethoxam and thiacloprid, was investigated in wastewater, aqueous extracts of sewage sludge and in aqueous surfactant solutions, which are abundant in wastewater. Dissipation in the dark was also studied in wastewater, due to reduction of transmitted sunlight in wastewater ponds. With regard to photolysis, thiamethoxam degraded rapidly in all the aqueous solutions. Among them sewage sludge extracts slightly modified (average half-life 17.6h), wastewater increased (13.7h) and non-ionic surfactants led, as a family, to the highest dissipation rates (average 6.2h), with respect to control water (18.7h). Additionally this pesticide also underwent a slower biodegradation process in wastewater in the dark under anaerobic conditions (around 25d). A metabolite of thiamethoxam from the biological decomposition in wastewater was identified by HPLC/MS. On the other hand thiacloprid was found to be resistant to photo- and biodecomposition and remained almost unchanged during the experimental periods in all the tested media.

Comparison of Two Wet Digestion Procedures for Multi‐element Analysis of Plant Samples

Two microwave digestion systems for multi‐element analysis of leaves and fruits were compared. Samples were digested by two different methods: 1) with HNO3 (8 mL) and HClO4 (6 mL) using an open microwave system and 2) with HNO3 (5 mL) and H2O2 (3 mL) in a closed microwave system. Total concentrations of aluminum (Al), cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), leaf (Pb), magnesium (Mg), manganese (Mn), nickel (Ni), and zinc (Zn) were determined in 22 samples by inductively coupled plasma atomic emission spectrometry and by simultaneous inductively coupled plasma mass spectrometry (ICP/AES and ICP/MS). Not statistical differences for Cu, Mn, Mg, Pb, and Zn concentration between the two methods were observed. Trace elements, whose concentration is low, such as Cr and Cd, have to be determinate by ICP/MS. The accuracy of the procedures was acceptable, except for Al, Fe, and Mg using the open microwave system, as the results from certified reference materials were in agreement with certified values.

Selective uptake of major and trace elements in Erica andevalensis, an endemic species to extreme habitats in the Iberian Pyrite Belt

To assess the ecophysiological traits and the phytoremediation potential of the endemic heather Erica andevalensis, we determined the concentrations of major and trace elements in different plant parts and in rizosphere soils from Riotinto mining district (Huelva, Spain). The results showed that E. andevalensis may grow on substrates with very high As, Cu, Fe and Pb concentrations (up to 4114, 1050, 71900 and 15614 microg/g dry weight, respectively), very low availability of macro- and micronutrients and with pH values ranging from 3.3 to 4.9. In these harsh edaphic conditions E. andevalensis selectively absorbed and translocated essential nutrients and excludes potentially phytotoxic elements, which were accumulated in the root epidermis. The concentrations of major and trace elements in E. andevalensis aerial parts from the Riotinto mining district were in the normal range for plants; likewise other Erica species it accumulated Mn and only in a very polluted site we measured leaf concentrations of As and Pb within the excessive or toxic limits for plants. Differently from previous studies, which emphasized the soil pH and bioavailability of phytotoxic elements as the main stress factors, this study showed that in the Riotinto region, E. andevalensis can tolerate wide range of pH and toxic element concentrations; the harshest environments colonized by monospecific patches of this species were characterized above all by very low availability of nutrients. The extraordinary capability to adapt to these extreme habitats made E. andevalensis a priority species to promote the phytostabilization and the development of a self-sustaining vegetative cover on Riotinto mine tailings.

Effects of silicon on copper toxicity in Erica andevalensis Cabezudo and Rivera: a potential species to remediate contaminated soils

The influence of silicon on responses to copper excess was studied in plants of Erica andevalensis. Plantlets were grown in nutrient solutions containing two Cu (1 and 500 µM) and three Si concentrations (0, 0.5 and 1 mM). Plant growth, water content, and mineral nutrient concentration were determined. Plants grown with 500 µM Cu showed differences in growth and shoot water content depending on Si supply. The addition of 1 mM Si in high-Cu nutrient solutions significantly improved plant growth and reduced water loss preventing plant death related to Cu-excess. Silicon supply reduced significantly leaf Cu concentration (up to 32%) and increased Cu concentration in roots. Phytoliths isolated from leaves were analysed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Such phytoliths consisted in silica deposits associated with Cu and other elements (K, Ca, P). Improvement by Si of Cu tolerance in E. andevalensis was clearly related to the inhibition of Cu upward transport. The leaf phytoliths formed in Si-treated plants might have some contribution to tolerance by Cu immobilisation and inactivation.

Desorption of two organophosphorous pesticides from soil with wastewater and surfactant solutions.

A batch test was used to evaluate the extent of desorption of diazinon and dimethoate, preadsorbed on a calcareous agricultural soil, representative of the Mediterranean area. Urban wastewater from a secondary treatment and seven surfactant solutions, at concentrations ranging from 0.75 mg L(-1) to 10 gL(-1), were used. The surfactants assayed were cationic (hexadecyl trimethyl ammonium bromide (HD)), anionic (sodium dodecyl sulfate (SDS), Aerosol 22 (A22) and Biopower (BP)), and nonionic (Tween 80 (TW), Triton X 100 (TX) and Glucopon 600 (G600)). Desorption of dimethoate was either not affected or only slightly by the nonionic and anionic surfactants tested, while desorption of diazinon from the soil was only enhanced by A22, BP and TW. This desorption increase correlated significantly with the surfactant concentration of the solution used for desorption and with the concurrent increase in the supernatant of the dissolved organic carbon, in particular that originating from the surfactant. This parameter did not vary with the use of SDS, G600 and TX. The cationic surfactant HD was retained on the soil surface, as confirmed by an increase in soil organic carbon, resulting in a fall in desorption rate for both pesticides. Comparing treatment by wastewater with control water, there was no difference in desorption rate for either pesticide. Mixed TW/anionic surfactant solutions either did not modify or slightly increased desorption of both pesticides in comparison with individual surfactant solutions.

Stress responses of Erica andevalensis Cabezudo & Rivera plants induced by polluted water from Tinto River (SW Spain).

The effects of Tinto River water on Erica andevalensis growth, biochemical indicators and elemental concentration and distribution were investigated under laboratory conditions. High levels of toxic elements such as B, Fe and S and acidic pH characterized the river water. Plant analysis revealed that the concentration of Al, B, S and Fe increased in all plant organs reaching in some cases values in the toxicity range. Plants transferred into river water stopped growing and stress was manifested by plant water loss, increase in peroxidase activity and decrease of chlorophyll a concentration. Significant decreases of free amino acid concentration were found in shoots and roots of plants grown in diluted river water. The results indicated that Tinto River water acidity and its excess in soluble elements produced altogether severe alterations in roots affecting plant water and nutrient uptake and leading to the massive entry of some metals (e.g. Fe, Al) with toxic effects. Scanning-electron microscopy (cryoSEM and ESEM) observations showed that E. andevalensis had not exclusion mechanisms of Cu, Fe and S therefore it was not able to reduce translocation to aerial parts.

Assessment of phenylurea herbicides sorption on various Mediterranean soils affected by irrigation with wastewater

The retention values of two herbicides, chlorotoluron and isoproturon, in five Mediterranean soils were assessed by two different approaches, a dynamic method, using a batch technique (BT) and a static method, using a soil saturated paste (SP). The SP method led in all cases to lower herbicide sorption when compared with BT, although pesticide distribution constants from both methods were linearly related for the set of used soils (R(2)⩾0.99) showing that both methods similarly reflected the behaviour of the different soils. Low-quality water, evaluated by employing recycled urban wastewater, did not modify herbicide sorption when compared with high quality water, in any soil and with any method.

Evaluation of Lead Toxicity in Erica andevalensis as an Alternative Species for Revegetation of Contaminated Soils

Although revegetation using native flora is a low cost way to stabilize soil and restore the landscape contaminated with metals, little is known regarding the Pb-tolerance of many of these species. For this purpose, we evaluated the tolerance of Erica andevalensis to Pb by growing plants in nutrient solutions with increasing concentrations of Pb (up to 100 μM). Plant growth and different physiological parameters were determined to ascertain tolerance to metal stress. Additionally, an electron microscopy study coupled with EDX-analysis was performed to get clues on the Pb uptake and translocation from roots into stem and leaves. The LOEC (the lowest observed effect concentration) of Pb was 40 μM while the IC50 (inhibition concentration) was 80 μM Pb. Chemical analysis revealed a root>stem>leaf accumulation pattern. There was a severe reduction in fresh biomass and chlorophyll concentration at the highest Pb dose. The SEM-EDX study indicated that Pb was mostly located in root epidermal tissues. The blockage of Pb on the root probably avoided its toxic effects by limiting Pb transport to other tissues.

Effect of two different composts on soil quality and on the growth of various plant species in a polymetallic acidic mine soil

The effect of the addition (0-10%) of two types of sewage sludge composts (composted sewage sludge [CS] and sewage sludge co-composted with olive prune wastes [CSO]) on a polymetallic acidic soil from the Riotinto mining area was evaluated by i) a soil incubation experiment and ii) a greenhouse pot experiment using tomato (Solanum lycopersicum Mill.), ryegrass (Lolium perenne L.) and ahipa (Pachyrhizus ahipa (Wedd.) Parodi). Compost addition improved the soil organic carbon content, increased the pH and the electrical conductivity and enhanced enzyme activities and soil respiration, more for CSO than for CS. Plant growth was generally enhanced after compost addition, but not proportionally to the dose. Foliar concentrations of some hazardous elements (As, Cr, Fe) in tomato growing in non-amended soil were above the thresholds, questioning the adequacy of using this plant species. However, leaf concentrations of essential and potentially toxic elements (Fe, As, Cr and Pb) in tomato and/or ryegrass were reduced after the amendment with both composts, generally more for CSO than for CS. Conversely, foliar concentrations in ahipa, a plant species which is able to grow without the need of compost addition, were safe except for As and were only slightly affected by compost addition. This plant species would be a suitable candidate due to its low requirements and due to the limited element translocation to the leaves. Concerning the composts, amelioration of plant and soil properties was better accomplished when using CSO, a compost of sewage sludge and plant remains, than when using CS, which only contained the sludge.

SOLUBLE METAL POOL AS AFFECTED BY SOIL ADDITION WITH ORGANIC INPUTS

The potential impact of diverse inputs of organic matter (hay, maize straw, and peat) on the mobility and bioavailability of Cd, Cu, Pb, and Zn was examined at laboratory scale for three soils with contrasting properties and for two moisture regimes: field capacity and saturated conditions. Soil solution was characterized for total soluble metals, dissolved soil organic carbon, and ultraviolet absorbance at 254 nm. Speciation analyses were performed with WHAM VI. For field capacity conditions, metal mobility increased (Pb>Cu>Zn>Cd) for all soils and treatments compared with controls and was significantly correlated (p<0.05) with dissolved organic matter (r=0.540). Solubilization of organic matter was mostly driven by Al mobilization (r=0.580, p<0.05) and variations in solution pH. The bioavailable pool of metals, estimated as free ion activities, decreased with the increasing occurrence of metal-organic matter complexes, which was accompanied by an increase in solution of highly aromatic organic matter. Soil saturation generally decreased metal mobility and the ratio of metal-organo matter complexes in solution. Consistently, such effects were accompanied by a decrease in the solubilization of organic matter and lower mobilization of Al, Fe, and Mn.