Accumulation of Cu, Cd, Pb, Zn and total P from synthetic stormwater in 30 bioretention plants

Removal effect of pollutants from stormwater runoff in shallow bioretention system with gramineous plants

The bioretention system is one of the most widely used low impact development (LID) facilities with efficient purification capacity for stormwater, and its planting design has been a hot spot for research at home and abroad. In this paper, ryegrass (Lolium perenne L.), bermuda (Cynodon dactylon Linn.), bahiagrass (Paspalum notatum Flugge), and green grass (Cynodon dactylon × C .transadlensis 'Tifdwarf') were chosen as plant species to construct a shallow bioretention system. The growth traits and nutrient absorption ability of four gramineous plants were analyzed. Their tolerance, enrichment, and transportation capacity were also evaluated to compare plant species and their absorptive capacity of heavy metals (Cu, Pb, and Zn). Results showed that the maximum absorption rate (Imax) ranged from 22.1 to 42.4 μg/(g·h) for P and ranged from 65.4 to 104.8 μg/(g·h) for NH4+-N; ryegrass had the strongest absorption capacity for heavy metals and the maximum removal rates of Cu, Pb, and Zn by four grasses were 78.4, 59.4, and 51.3%, respectively; the bioretention cell with ryegrass (3#) was significantly more effective in purifying than the unplanted bioretention cell (1#) during the simulated rainfall test. Overall, the system parameters were optimized to improve the technical application of gramineous plants in the bioretention system.

Evaluating bioretention scale effect on stormwater retention and pollutant removal

Bioretention column studies are commonly used in laboratory to assess the performance of such structures in removal of pollutants and to investigate different conceptions aiming to increase their efficiency. However, no studies were found recommending suitable diameters or sizes, or about the uncertainties related to the transfer of results among the different scales (i.e., among different experiments or from the laboratory to field scale). This study assessed the effect of the varying diameters in experimental bioretention columns on the retention and removal of pollutants from stormwater runoff. Three sets of columns with diameters of 400 mm, 300 mm, and 200 mm were assessed. The results showed that runoff retention (R) was affected by the time interval between stormwater events, but not by the bioretention diameter, although the diameter influenced the variability of R results. The removal of TSS (95%), nitrite (98%), and phosphate (96%) did present variability among the different bioretention diameters. However, the nitrate removal was statistically different among the bioretention columns, with removal efficiency above 50% in the 300-mm and 200-mm columns, while the 400-mm columns acted as a source of nitrate by increasing its concentration in the outflow stormwater by up to 285%, suggesting that the removal of this pollutant can be influenced by the scale effect of the bioretention columns and the experiments with small bioretention diameters may not provide reliable results.

Dodonaea viscosa (Sapindaceae) as a phytoremediator for soils contaminated by heavy metals in abandoned mines

Dodonaea viscosa (L.) Jacq. is a plant with a wide distribution that expands throughout almost all Mexican territory and is used in traditional medicine to treat many ailments. This species has been found associated with polluted areas, including mine tailings. Huautla, Morelos, Mexico, was a metallurgic district where mining activities generated 780,000 tons of waste rich in metals, deposited at 500 m from the town without any treatment; this situation has been related to different environmental threats and human health risks. The study was carried out for 18 months on seedlings developed under greenhouse conditions in two treatments: control substrate and mine tailings substrate. The concentration of six metals (Cd, Cr, Cu, Fe, Pb, and Zn) was measured through atomic absorption spectrophotometry in plant tissues, roots, and leaves. Effects of metal exposure were analyzed by size, micro-morphological character changes, and genetic damage in foliar tissue using the comet assay. The results showed significantly higher metal concentrations in the roots and leaves of individuals growing on the mine tailing substrate in comparison to the same plants tissues growing on control substrate. Positive and significant relationships between exposure time and metal concentration in roots and leaves, and between metal bioaccumulation in leaves and genetic damage were registered. Four out of six micro-morphological and size characters evaluated decreased significantly in exposed plants, except for stomatic index and root biomass. The most important metals in terms of the number of significantly affected micro-morphological and size characters showed the next pattern: Fe > Cd = Cr = Pb > Cu > Zn. D. viscosa is an efficient accumulator of Cu, Cd, Fe, Pb, and Zn in its root and leaf tissues. Overall, metal translocation factors in exposed D. viscosa plants showed the following pattern: Zn > Cu > Cd. We conclude that D. viscosa has the potential to phytoextract (Zn, Cu, and Cd), and phytostabilize (Cu, Cd, Fe, Pb, and Zn) metals from polluted soils, and along with its abundance, natural establishment in mine tailings, high levels of metal translocation, and bioconcentration factors, without affecting plant development, it can be an ideal candidate for phytoremediation of metal polluted soils.

Setting-up of different water managements as mitigation strategy of the environmental impact of paddy rice

Northern Italy represents the most important rice-growing district in Europe. In this area, rice is the main annual crop and the main revenues source for farmers. However, Italian climatic condition led to a traditional cultivation characterized by continuous flooding, causing emissions of methane into the atmosphere due to the organic matter fermentation in anaerobic conditions, and, consequently, a high environmental impact. The water conditions of paddy fields also affect heavy metals uptake by rice plants. In this context, this study focuses on the evaluation of environmental impact and of heavy metal content in paddy rice, and it may represent an important step in mitigating the environmental impact of rice production. In detail, this study quantifies the environmental benefits related to the adoption of an alternative water management characterized by an additional aeration period during stem elongation. To this purpose, field trials were carried out and the Life Cycle Assessment (LCA) approach was applied with a cradle-to-farm gate perspective. The potential environmental impact of the production of two rice varieties (Carnaroli and Caravaggio) was analysed in terms of 12 different impact categories and dehulled rice grain were analysed for arsenic and cadmium content. Alternative flooding decreases CH₄ emissions in all cases evaluated (from 15% to 52%), resulting in a reduction in the climate change impact of rice cultivation (from 12% to 32%). Furthermore, the alternative water management does not influence grain yield and it reduces all the other environmental impact categories in 2 out of 4 cases. Regarding the heavy metals contents, the arsenic content in the grain decreases in all alternative scenarios, whereas the cadmium content increases, while remaining well below the legal limits.

Morphological, physiological, and genotoxic effects of heavy metal bioaccumulation in Prosopis laevigata reveal its potential for phytoremediation

Mining industry generates large volumes of waste known as mine tailings, which contain heavy metals (HMs) that generate a risk to environmental health. Thus, remediation of HM pollution requires attention. In this study, HM bioaccumulation, genotoxic damage, and morphological and physiological changes in the tree species Prosopis laevigata were evaluated in order to assess its potential for remediation of mine tailings. P. laevigata plants were established in two treatments (reference substrate and tailing substrate) under greenhouse conditions. Every 2 months, six individuals were selected per treatment for 1 year. From each individual, macromorphological (height, stem diameter, and number of leaves), micromorphological (stomatal coverage and stomatal index), and physiological parameters (chlorophyll content) were evaluated, as well as the concentration of Pb, Cu, Cd, Cr, Fe, and Zn in root and foliar tissue. Genetic damage was assessed by the comet assay in foliar tissue. These parameters were evaluated in adult individuals established in mine tailings. Roots bioaccumulated significantly more HM compared to foliar tissue. However, the bioaccumulation pattern in both tissues was Fe > Pb > Zn > Cu. The plants in tailing substrate reduced significantly the morphological and physiological characters throughout the experiment. Only the bioaccumulation of Pb affected significantly the levels of genetic damage and the number of leaves, while Zn reduced plant height. The percentage of plants that have translocation factor values greater than 1 are Cu (92.9) > Fe (85.7) > Pb (75.0) > Zn (64.3). P. laevigata has potential to phytoremediate environments contaminated with metals, due to its dominance and establishment in abandoned mine tailings, and its ability to bioaccumulate HM unaffecting plant development, as well as their high levels of HM translocation.