Silvana Arreghini

Phytoremediation of two types of sediment contaminated with Zn by Schoenoplectus americanus

The effect of different sediments on growth, Zn uptake, Zn plant distribution, and morphometric variables of Schoenoplectus americanus were investigated under controlled conditions. Two types of sediments were assayed: from a large natural levee (LS) and alluvial sediments (AS), the former with lower organic matter (OM) and nutrients content than AS, without and with added Zn (2500 μg Zn/g air-dry sediment). Zinc partition in sediment was determined. Increases in water conductivity and Zn concentrations in water and sediments were observed in artificially contaminated treatments. Plants showed a lower aboveground growth rate, height, and width of shoots, and a higher Zn concentration in shoots and rhizomes. In the contaminated treatments, AS treatment showed lower Zn concentration in water and higher Zn concentration in sediments (total, exchangeable, and OM fractions) than LS treatment, due to Zn displacement from floodwater to sediments. The presence of a high level of OM and nutrients also increased aboveground biomass growth, whereas it decreased Zn concentration in shoots. Although the translocation factor increased with Zn addition, it was lower in AS treatment. Sediments of AS treatments are a suitable environment for growth of S. americanus, which partially compensates the toxic effects of Zn. Our results provide an encouraging basis for planning larger scale experiments to test the role of OM and nutrients in improving phytoremediation.

On-Site and Full-Scale Applications of Phytoremediation to Repair Aquatic Ecosystems with Metal Excess

There are a few studies about full scale and on-site treatments using macrophytes. In this contribution we compare the phytoremediation role of floating, submersed, and emergent macrophytes grown in natural and artificial wetlands. Metal uptake capacity of aquatic plants is low and this exclusion strategy seems to be more widespread among aquatic plants. Bioconcentration factors and translocation are lower than those calculated in bioassays conducted under laboratory conditions. There are not hyperaccumulators among the studied plants. However, regarding the capacity of accumulation of metals in the standing crop, the floating plants are most effective for phytoextraction, followed by submersed species and then emergent species. The emergent plants are more effective for phytostabilization. The metals released during the decomposition could be further retained by the new binding sites generated in bottom sediment. Use of native species in remediation projects, not always considered in scientific or technical papers is essential to preserve biological diversity and, requires more detailed studies for each natural ecosystem.

Impact of the Moron stream on water quality of the Reconquista River (Buenos Aires, Argentina)

The Reconquista River basin is located in an urban area where 2.5 10 6 inhabitants and 4,242 industries are settled. The confluence with the Moron stream shows the largest anthropogenic impact. The effect of the Moron stream on the water quality of the Reconquista River was evaluated in relation to its organic, mineral and metal contribution. Bimonthly samplings were carried out in the Reconquista River upstream (GOR), and downstream (SMT) from the confluence with the Moron stream and in the latter (MOR). Dissolved oxygen, pH, conductivity, temperature, transparency, nutrients, major ions, suspended solids, particulate and total organic carbon, Kjeldahl nitrogen, total phosphorus and heavy metals were determined in water samples. Discharge ratios between the Reconquista and Moron streams were estimated based on chloride concentrations. The samplings were ordered from the Principal Component Analysis in: GOR, SMT and MOR according to a growing gradient of organic and mineral contamination. This gradient has a spatial component (related to the discharge point of the Moron stream) and one related with the flow of the Reconquista River. Mean levels of heavy metals were higher than the thresholds for aquatic life protection. The most important were: lead, zinc, copper and mainly chromium, all of them related to industrial activity. Their concentrations responded to an irregular and intermittent discharge. Sometimes, metal levels at SMT and GOR were higher than at MOR, indicating other sources of contamination besides the Moron stream.

Shoot litter breakdown and zinc dynamics of an aquatic plant, Schoenoplectus californicus

ABSTRACT Decomposition of plant debris is an important process in determining the structure and function of aquatic ecosystems. The aims were to find a mathematic model fitting the decomposition process of Schoenoplectus californicus shoots containing different Zn concentrations; compare the decomposition rates; and assess metal accumulation/mobilization during decomposition. A litterbag technique was applied with shoots containing three levels of Zn: collected from an unpolluted river (RIV) and from experimental populations at low (LoZn) and high (HiZn) Zn supply. The double exponential model explained S. californicus shoot decomposition, at first, higher initial proportion of refractory fraction in RIV detritus determined a lower decay rate and until 68 days, RIV and LoZn detritus behaved like a source of metal, releasing soluble/weakly bound zinc into the water; after 68 days, they became like a sink. However, HiZn detritus showed rapid release into the water during the first 8 days, changing to the sink condition up to 68 days, and then returning to the source condition up to 369 days. The knowledge of the role of detritus (sink/source) will allow defining a correct management of the vegetation used for zinc removal and providing a valuable tool for environmental remediation and rehabilitation planning.