Potentially toxic elements capture by an active living wall in indoor environments: Effect of species in air phytoremediation.

Indoor air pollution is a serious health problem throughout the world. Plants are known to be able to reduce the effect of air pollution and improve indoor air quality (IAQ). The aim of the present study was to compare the effectiveness of four plant species (Tradescantia zebrina hort. ex Bosse, Philodendron scandens K. Koch & Sello, Ficus pumila L. and Chlorophtytum comosum (Thunb.) Jacques) planted in an active living wall (ALW) for capturing particle pollutants. The ALW was introduced in a glass chamber and exposed to large (10-40 µm) and fine (1.2-10 µm) airborne particles containing a fixed concentration of potentially toxic elements (Al, B, Cd, Co, Cr, Cu, Ni and Pb). The surface particle deposition (sPM) was estimated in the leaves from the four species and the potentially toxic element concentration in the particulate matter (PM) was measured in plants, medium culture and in the ALW support system. The distribution of different particle size fractions differed between species. The capacity to trap particles on leaf surfaces was similar among the species (4.7-13 ng cm-2) except when comparing Tradescantia and Chlorophytum with Ficus, being higher in the latter species. Differences in toxic elements accumulation capacity were observed between species depending on the elements considered. The percentage of reduction in indoor pollution using an ALW was in a range of 65-79% being similar between species. Plants were the most important component of the ALW in terms of accumulation of indoor potentially toxic elements. The data presented here could be used to model the effectiveness of ALW systems schemes in improving IAQ.

Soil-plant system and potential human health risk of Chinese cabbage and oregano growing in soils from Mn- and Fe-abandoned mines: microcosm assay.

In Portugal, many abandoned mines are often close to agricultural areas and might be used for plant food cultivation. Soils in the vicinity of two Mn- and Fe-abandoned mines (Ferragudo and Rosalgar, SW of Portugal) were collected to cultivate two different food species (Brassica rapa subsp. pekinensis (Lour.) Hanelt and Origanum vulgare L.). Chemical characterization of the soil-plant system and potential risk of adverse effects for human health posed by plants associated with soil contamination, based on the estimation of hazard quotient (HQ), were assessed in a microcosm assay under greenhouse conditions. In both soils, the average total concentrations of Fe and Mn were above the normal values for soils in the region and their concentration in shoots of both species was very high. Brassica rapa subsp. pekinensis grew better in Ferragudo than in Rosalgar soils, and it behaved as an excluder of Cu, Mn, Fe, S and Zn in both soils. The HQ for Cu, Fe, Mn and Zn in the studied species grown on both soils was lower than unit indicating that its consumption is safe. The high Mn tolerance found in both species might be due in part to the high contents of Fe in the soil available fraction that might contribute to an antagonism effect in the uptake and translocation of Mn. The obtained results emphasize the need of further studies with different food crops before cultivation in the studied soils to assess health risks associated with high metal intake.

Phytostabilization potential of Erica australis L. and Nerium oleander L.: a comparative study in the Riotinto mining area (SW Spain).

Phytostabilization is a green, cost-effective technique for mine rehabilitation and ecological restoration. In this study, the phytostabilization capacity of Erica australis L. and Nerium oleander L. was assessed in the climatic and geochemical context of the Riotinto mining district, southwestern Spain, where both plant species colonize harsh substrates of mine wastes and contaminated river banks. In addition to tolerating extreme acidic conditions (up to pH 3.36 for E. australis), both species were found to grow on substrates very poor in bioavailable nutrients (e.g., N and P) and highly enriched with potentially phytotoxic elements (e.g., Cu, Cd, Pb, S). The selective root absorption of essential elements and the sequestration of potentially toxic elements in the root cortex are the main adaptations that allow the studied species to cope in very limiting edaphic environments. Being capable of a tight elemental homeostatic control and tolerating extreme acidic conditions, E. australis is the best candidate for use in phytostabilization programs, ideally to promote early stages of colonization, improve physical and chemical conditions of substrates and favor the establishing of less tolerant species, such as N. oleander.

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.

Response of drought and fertilization in Erica andevalensis seed banks: significance for conservation management.

The present study attempts to investigate the size, composition and seedling dynamics of the seed bank of a metalliferous and vulnerable species, Erica andevalensis. Samples were taken during spring and autumn from two different sites. We also studied the effects of nutrient solution, irrigation from the river Tinto and irrigation deficit on seeding establishment and survival. Only E. andevalensis and Poaceae species emerged from the seed banks, although the former was dominant (98%). Germination and seedling establishment was totally inhibited by the waters of the river Tinto. Seed density was high in the soils of both seed banks irrigated with water and nutrient solution. We found no seasonal differences in the seed bank and number of germinated seeds and mortality rate and density were similar. From the standpoint of restoration management, the results indicate that the seed bank is a very important factor for successful species establishment.

Tolerance to high Zn in the metallophyte Erica andevalensis Cabezudo & Rivera.

The tolerance to high Zn was studied in the metallophyte Erica andevalensis Cabezudo & Rivera grown in nutrient solutions at different Zn concentrations (5, 500, 1,000, 1,500 and 2,000 µM Zn). Plant growth and nutrient uptake were determined. Metabolic changes were assessed by the analysis of peroxidase activity, organic metabolites related to metal chelation (amino acids, organic acids (malate, citrate) or protection (polyamines). While plants tolerated up to 1,500 µM Zn, despite presenting of low growth rates, the concentration of 2,000 µM Zn was toxic producing high mortality rates. Roots accumulated high Zn concentration (11,971 mg/kg) at 1,500 µM external Zn) apparently avoiding metal transfer into shoots. After 30 days of treatment with high Zn (1,000 and 1,500 µM Zn), the leaves accumulated high levels of glutamine. Short-term treatment with 500 µM Zn, significantly increased the concentration of asparagine and glutamine in roots. Citrate concentration was also considerably increased when exposing roots to Zn excess. Metal immobilization in the root system, low interference with the uptake of nutrients and an increased production of putative organic ligands (amino acids, citrate) might have provided the Zn tolerance displayed by Erica andevalensis.

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 microM). 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 microM while the IC50 (inhibition concentration) was 80 microM 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.

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.

Accumulation and in vivo tissue distribution of pollutant elements in Erica andevalensis.

Erica andevalensis is an endemic shrub from an area in the southwest of Spain (Andalucia) characterized by acidic and contaminated soils. Scanning electron microscopy (SEM) of samples after conventional or cryo-fixation preparation protocols was used for morphological and anatomical studies. SEM coupled with EDX-analysis was employed to localise and quantify different elements within plant parts (leaves, stems and roots) in samples collected in the field. Morphological studies revealed that the species has typical adaptive structures to drought-stress such as rolled needle-like leaves, sunken stomata and a thick waxy cuticle on the upper epidermis. Roots were associated with fungi which formed intra and extra-cellular mycelia. The SEM studies showed that Cu was not sequestrated into the root tissues and was uniformly distributed in leaf tissues. Meanwhile, Pb was only localised within epidermal root tissues which indicates that its sequestration in an external matrix might represent a tolerance mechanism in this species. Iron was uniformly distributed throughout the leaves, while in roots it was predominantly retained on the epidermal cell walls. The exclusion and tolerance mechanisms adopted by this species to survive in mining areas indicate that it can be used successfully in the re-vegetation of contaminated areas.

Assessment of airborne heavy metal pollution by aboveground plant parts.

Italian stone pine (Pinus pinea L.) and oleander (Nerium oleander L.) leaves, bark and wood samples were collected at different sites around an industrial area (Huelva, SW Spain) and compared with samples of the same species from a background site. Samples were analysed with respect to the following pollutants: Al, Ba, Cr, Cu, Fe and Pb by ICP-AES. The suitability of different plant parts as biomonitors of pollution was investigated. In pine samples from the polluted sites the ratio of concentrations between bark and wood was high for Al, Ba, Cu and Fe, whereas no differences were found in samples from the unpolluted area. No differences were detected in oleander for the same ratio. In the oleander species, the ratio between leaves and wood concentration allowed to distinguish between control and polluted sites. The ratio of the concentration between leaves and wood was elevated for Al, Ba and Fe in pine samples from the polluted sites. The ratio of the concentration in bark or leaves to their concentration in wood might be useful to detect inorganic atmospheric pollutants.

The composition and relationships between trace element levels in inhalable atmospheric particles (PM10) and in leaves of Nerium oleander L. and Lantana camara L.

In order to evaluate the composition of inhalable atmospheric particles and to study the relationship between trace element levels in PM10 and in leaves of two plant species, the amount of Ba, Cu, Fe, Mn, Pb, Ti and V were analysed in PM10 and in Nerium oleander L. and Lantana camara L. leaves from two sites in the city of Seville and one remote control site. In PM10, the Cu and Fe content was significantly lower (p<0.05) in the control site than in the other sites. No correlations between leaf content and air content were found for the elements in L. camara. On the contrary, positive and significant correlations (p<0.05) were found between leaf content of N. oleander and PM10 content for Cu and Fe. The data suggest that N. oleander can be used in atmospheric biomonitoring studies, because it is especially useful for Cu and Fe, N. oleander being a better indicator than L. camara.