Scientists working to produce environmentally safe pesticides

Specialists of the Institute of Biophysics (Siberian Branch, Russian Academy of Sciences), Siberian Federal University and Institute of Forest (Siberian Branch, Russian Academy of Sciences) are working to produce environmentally safe pesticides. New preparations are a mixture of pesticides with biodegradable polymers. Polymers gradually degrade in the soil, and pesticides get slowly released and get exactly in the place where they were deposited.

Pesticides are hundreds of active substances and dozens of thousands of preparations. Contemporary pesticides are used in the form of powder and emulsions; under the influence of precipitations and wind they do not only get to their destination but also disperse at large areas thus contaminating environment. Unfortunately, it is sometimes rather difficult to identify their presence in water, soil and air, besides little is known about toxic properties of multiple preparations and about consequences of their longstanding influence on the environment. For this reason contemporary pesticides are dangerous for people and environment. At that, they do not perform their immediate task - they do not protect plants from vermin, a lot of which have developed resistance to pesticides. Therefore, agriculture needs fundamentally new protection, which could enable address delivery of chemicals.

To this end, the pesticide is enclosed into a matrix made of biodegradable materials. The pesticide enclosed in such a matrix will not get into water or air, it will remain where it was deposited ('packed') and will gradually release from the polymer carrier. In some countries, ethyl-cellulose, polyurethane and sodium alginate are already used for this purpose. The researchers from Krasnoyarsk suggest to use for pesticide depositing the polymer of microbiological origin actively degradable in the soil (copolymer of hydroxybutyrate and hydroxyvalerianate), which was synthesised at the Institute of Biophysics of the Earth (Russian Academy of Sciences). This polymer fully degrades under the influence of soil microorganisms, therefore it is not accumulated either in soil or in water and does not contaminate outskirts like plastic bottles do. Destruction takes place within several months, which allows to develop preparations of lasting action.

The researchers have tested two preparations. One of them, a complex action insecticide - a-hexachlorocyclohexane - is used to fight harmful insects and utilised for seed sterilisation to protect sprouts from soil vermin. The other chemical - Lindane - is an efficient insecticide with a wide action spectrum. The preparations were mixed with well-milled powdery polymer, and tablets (which are 3 millimetres in diameter, their weight making 20-22 grams) were pressed out of obtained mixture. Preliminary weighed samples were deposited into the lawn-and-garden soil and kept there for 12 weeks at a definite temperature and humidity, periodically taking samples to determine remaining mass of the polymer and pesticide concentration in the soil.

Soil microorganisms perceived the polymer as a nutritious product and actively destroyed it. The bulk of the polymer was destroyed in the soil within 40 to 50 days since the begging of the experiment, by that time, there remained no more than 5% of head grade in the tablet. Pesticides got out of the tablets into the soil unhurriedly. During the first 30 to 40 days, no more than 2% to 3% of a-hexachlorocyclohexane was released, and in 70 to 80 days, the tablet was released of 10% to 12% of the preparation. The Lindane output, the content of which was higher in the polymer matrix, was about 30% by the end of the experiment.

By the example of two pesticides the researchers have proved that the preparations enclosed into a biodagragable polymer matrix are leaving it gradually, without abrupt discharges. By varying the polymer/preparation ratio, the researchers can regulate the rate of pesticide release into the soil.