Assessment of metal/metalloid occurrence in rivers with their accumulation in macrophyte case study with Myriophyllum alterniflorum.

Water quality monitoring with integrative tools is a main issue of concern for environment assessment. Submerged aquatic macrophyte can be a good candidate for the evaluation of contaminant content in rivers. Indeed, owing to their habitat, aquatic macrophytes interact directly with surface water; they can absorb contaminants and thus allow to detect their presence in water. In situ studies were conducted over 28 days in five aquatic environments, affected by different levels of anthropogenic pressure (domestic wastewater plant, industrial activities), during two field campaigns. We have investigated whether the accumulation of some metals and a metalloid (As) in Myriophyllum alterniflorum could be used to detect their occurrence in river waters. Our results demonstrated that long time bioaccumulation was correlated with the contaminant levels in water. However, the water composition and the duration of exposure affected the studied pollutants' absorption. On an operational point of view, the optimal duration of exposure of Myriophyllum alterniflorum to assess the water quality is conditioned by the contaminant contents in waters that can induce different defense mechanisms as the reduction of pollutant absorption and their efflux. In addition, the nutrient concentration influenced the accumulation of pollutants since the higher the nutrient level, the higher the essential metal accumulation was observed.

Are Myriophyllum alterniflorum biomarker responses to arsenic stress differentially affected by hydrodynamic conditions?

Arsenic (As) is a significant contaminant in the environment and its detection through macrophytes can provide a powerful tool. Myriophyllum alterniflorum constitutes a good candidate by virtue of its ability to accumulate contaminants, and moreover its biomarkers can respond to the presence of trace metals and metalloids. The objective of this study therefore is to evaluate the watermilfoil response to As exposure under several hydrodynamic conditions since it is well known that hydrodynamics affect plant functioning. For this purpose, fresh watermilfoil plants are subjected to three hydrodynamic conditions, namely laminar, turbulent and calm, in a synthetic medium either enriched or not by 100 µg.L-1 arsenic for 21 days. Growth, pigment content (chlorophyll a, b and carotenoids), respiratory and photosynthetic activities, osmotic potential and hydrogen peroxide concentration are all monitored. Arsenic accumulation is measured separately in the roots and shoots of Myriophyllum alterniflorum. On the one hand, it should be noted that arsenic induces: (i) a significant increase in H2O2 content; (ii) a decrease in osmotic potential, pigment content, photosynthesis and respiration rates, shoot and root growth; and (iii) an inhibition of shoot branching. Moreover, a higher accumulation of this metalloid in roots than in shoots, regardless of the hydrodynamic condition, is witnessed. While on the other hand, hydrodynamic conditions only affect watermilfoil morphology and arsenic accumulation. Also, the younger and older parts have experienced differential toxic effects. Overall, our results suggest the effective use of M. alterniflorum in both water quality biomonitoring and phytoremediation studies.

Comparative in vitro/in situ approaches to three biomarker responses of Myriophyllum alterniflorum exposed to metal stress.

Surface water pollution by trace metal elements constitutes problems for both public and terrestrial/aquatic ecosystem health. Myriophyllum alterniflorum (alternate watermilfoil), an aquatic macrophyte known for bioaccumulating this type of pollutant, is an attractive species for plant biomonitoring within the scope of environmental research. The two metal elements copper (Cu) and cadmium (Cd) are considered in the present study. Cu is essential for plant development at low concentrations, while very high Cu concentrations are detrimental or even lethal to most plants. On the other hand, Cd is usually toxic even at low concentrations since it adversely affects the physiological plant functions. In order to check whether watermilfoil could be used for the in situ biomonitoring of Cu or Cd pollution in rivers, the plant biomarker sensitivity is first tested during long-term in vitro assays. Three markers specific to oxidative stress (glucose-6-phosphate dehydrogenase, malondialdehyde and α-tocopherol) are evaluated by varying the pollutant concentration levels. Given the absence of effective correlations between Cu and all biomarkers, the response profiles actually reveal a dependency between Cd concentration and malondialdehyde or α-tocopherol biomarkers. Conversely, preliminary in situ assays performed at 14 different localities demonstrate some clear correlations between all biomarkers and Cu, whereas the scarcity of Cd-contaminated rivers prevents using the statistical data. Consequently, the three indicated biomarkers appear to be effective for purposes of metal exposure analyses; moreover, the in situ approach, although preliminary, proves to be paramount in developing water biomonitoring bases.

Combined effect of copper and hydrodynamic conditions on Myriophyllum alterniflorum biomarkers.

The aim of this study is to determine the combined effect of copper and hydrodynamic conditions on the response of certain biomarkers of an aquatic macrophyte, namely Myriophyllum alterniflorum. Watermilfoil biomarkers are monitored in a synthetic medium enriched or not with copper (100 µg.L-1) for 21 days in aquarium systems (150 L), under three hydrodynamic conditions: laminar, turbulent, and calm. The studied biomarkers are: respiratory and photosynthetic activities; concentrations of chlorophyll a, b and carotenoids; osmotic potential; hydrogen peroxide content; and growth. In addition, Cu contents in water and in Myriophyllum alterniflorum (roots and shoots) are investigated. The hydrodynamic conditions only affect watermilfoil morphology. Copper accumulates less in turbulent zones; moreover, it is more likely to accumulate in shoots than in roots, except within the calm zone. Cu leads to: i) a significant increase in H2O2 content, ii) a decrease in root growth, pigment content, osmotic potential, photosynthesis and respiration rates, and iii) an inhibition of shoot branching. Differential effects are also observed between younger and older parts, thus indicating the benefit of considering these two plant parts separately in water quality biomonitoring.

Micropropagation of Myriophyllum alterniflorum (Haloragaceae) for stream rehabilitation: first in vitro culture and reintroduction assays of a heavy-metal hyperaccumulator immersed macrophyte.

Nowadays, submersed aquatic macrophytes play a key role in stream ecology and they are often used as biomonitors of freshwater quality. So, these plants appear as natural candidates to stream rehabilitation experiments. Among them, the stream macrophyte Myriophyllum alterniflorum is used recently as biomonitor and is potentially useful for the restoration of heavy-metal contaminated localities. The best way to obtain a mass production of watermilfoil plants is micropropagation. We developed in vitro culture of M. alterniflorum and the effects of five media on the plant development were assessed. Five morphological and four physiological endpoints were examined leading to the recommendation of the Murashige and Skoog medium for ecotoxicological studies on chlorophyllous parts, and of the Gaudet medium for root cytotoxicity and phytoremediation studies. Micropropagated clones were acclimatized in a synthetic medium and in situ reintroduction was performed efficiently. This is the first report of micropropagated plants transplantation in streams. The successful establishment of watermilfoil beds even in polluted areas strongly suggested that ecological restoration using micropropagated watermilfoil is a promising biotechnology for phytoremediation and rehabilitation of degraded areas. Moreover, high bioconcentration factors evidenced that watermilfoil hyperaccumulates Cd and Cu, and could be potentially used in phytoremediation studies.

The detection of snail host habitats in liver fluke infected farms by use of plant indicators.

Field investigations in 361 liver fluke infected cattle- or sheep-breeding farms on acid soil were carried out during thirty years in March and April to record indicator plants in relation to the category of site colonized by the intermediate host of liver fluke, the snail Galba truncatula. Seven types of snail zones and six species of indicator plants were recorded in the 7709 positive sites studied. The most frequent habitats were located at the peripheral extremities of open drainage furrows. Juncus acutiflorus, Juncus effusus, Glyceria fluitans, and Agrostis stolonifera were the indicator plants. Plant indicators were highly efficient (38-80% of variance explained) when used with the size of site area within a hydrographical zone. The identification of positive sites for G. truncatula is a key for controlling the intermediate host on pastures through biological control with predatory molluscs. The positive sites may be detected using a two-step method including first categorization of hydrographical zones and then, within a zone, use of one or several indicator plants (frequently J. acutiflorus).