Phytoremediation for Hg- and As-Contaminated Water

Novosibirsk State University has hosted research on plants which store heavy metals in their tissue and thus reduce industrial wastes in water and soil. Such a plant-based approach to clean up our environment is called phytoremediation, and NSU researchers have already identified some of the most effective plants. They were planted into a stream flowing to the River Ur in Kemerovskaya region in order to absorb mercury (Hg).

An assistant at the Chair of Environmental Chemistry and a postgraduate student at the Nikolaev Institute of Inorganic Chemistry, SB RAS, Tamara Romanova tells us about her work.

As we all know, Siberia hosts numerous industrial factories and mines that emit a lot of industrial wastes, toxins, and byproducts at harmful levels. They oxidize and contaminate our air, water and soil.

The site for experiments was a tailings storage facility on the River Ur, which is used to store the materials left over after the process of separating the valuable fraction from the uneconomic fraction of ore, as it contained significant amounts of mercury. Chemists decided to solve the problem in collaboration with geologists and biologists by planting the water hyacinth from the greenhouses of the Institute of Cytology and Genetics, SB RAS, as well as some pond grass and cat’s tail, which are typical for the area.

Tamara Romanova says that the water hyacinth, with its tops on the surface and roots in the water, grows a huge biomass that absorbs all the contaminants. The absorption is so intensive that detoxification is highly effective. The pond grass is also well known for accumulating a wide range of elements. Such water growing plants are especially good at accumulating mercury. The plants' ability to tolerate what they've taken in is also remarkable.

Research in this field gives vast opportunities to apply phytoremediation in particular circumstances and to effectively detoxify, or remediate, soil or water. Moreover, we can collect the biomass and burn it in order to use the soot to extract the accumulated elements

Roughly speaking, we could obtain the elements that the plants had stored and reuse them. Of course, we should have significant amount of soot at our disposal, says the scientist, but some methods to extract elements in such a way have already been patented. According to our data, the plants growing in the Ur tailings facility could give us some barium (Ba). We are experimenting with silver and gold as well, which are present in ore concentrations. The economic benefits are obvious.

Tamara Romanova is currently working on her Ph.D. on this theme and is developing approaches to identify the ways of plants’ fixing mercury. She uses a set of analytical methods, such as effective liquid chromatography and element-selective detection, induced plasma atomic emission spectrometry, stripping voltammetry.

She says that it is not enough to detect that the water, for example, is contaminated with a certain element. We should find out the form of the element fixation. A certain mercury ion can well be harmless for people. However, some microorganisms can cause methylation, and the mercury turns into its organic form, which is much more hazardous for people and animals.

Another problematic area is to design a device that could kill two birds with one stone through analyzing compounds chromatographically and at the same time detecting the elements and their concentration. Standard equipment can do it, but only separately. Tamara says that together with her supervisor at the Institute of Inorganic Chemistry Olga Shuvaeva they are trying to mate the analyzer with a powerful detector. It is one of the challenges they face.

In addition, Tamara and her colleagues from the Voevodsky Institute of Chemical Kinetics and Combustion, SB RAS, collaborate with Chinese scientists who do research on the forms of arsenic (As). China suffers from arsenic-contaminated water, but what form of arsenic is it? Arsenic trioxide is known to be more toxic than arsenic pentoxide. Our exploratory work helps to identify particular forms of arsenic fixation, explains Tamara Romanova.

Prepared by Marina Moskalenko

Photos provided by Tamara Romanova