Pathways of migration persistent pesticides through chains of terrestrial and aquatic ecosystems

Introduction. The problem of studying the impact of pesticides on natural ecosystems and people's health has become particularly acute due to their widespread use in agriculture. Danger of pesticides is in their high biological activity, mobility in the natural environment and the ability to accumulate and to retain toxic properties for a long time. Different ways of migrating pesticides are possible, all starting with the dispersion of the drug in the environment, on the soil and plants during the processing of crops. The study of migration routes and toxic effects of pesticides on living organisms in biocenosis is important for organizing the necessary measures for environmental protection. The aim of the study. Considering possible ways of migration of steady pesticides through trophic chains of terrestrial and aquatic ecosystems to substantiate the model of predicted movement of pesticides for the development of tools for assessing their ecological hazard. Materials and methods. An important complex indicator that can be used to characterize the influence of a toxicant on an object is its accumulation ratio, as well as the transfer coefficient. Results and discussion. The laws of the migration of toxic substances by trophic (food) chains are important. There are usually several parallel food chains with possible interconnections in biocenosis that ensure its integrity and dynamism. In the case of terrestrial ecosystems, in particular meadow ecosystems and agrocenoses, the entry of substances (pesticides) into plants occurs due to surface adsorption of leaves and stems, as well as root-system absorption. That is, there are two main types of substances entering the plants: extra root and root. The further entry of pesticides into the human body occurs because of direct intake of plants or their fruits, as well as products of livestock derived from animals fed on contaminated plants. When distributing pesticides in water, an extremely important role plays the biota (hydrofauna and hydroflora). The principle of migrating of pesticides from the atmosphere, surface runoffs, groundwater, etc. into the rivers, is their number, physical and chemical properties of pesticides and water, the possibility of formation of bottom sediments, etc. Pesticides that have fallen into marine (ocean) ecosystems by air, are relatively evenly distributed among the main components - water and marine biota (plants, animals and microorganisms). Those who have fallen into the river drains are mainly concentrated in river flow. The migration of pesticides by trophic chains is a rather complicated process, which depends on many factors. These include, in particular, the physical and chemical properties of substances themselves and of soil, water, air, etc., the effects of abiotic (temperature, humidity, etc.) and biotic factors (soil and aquatic microorganisms and other organisms that are capable of accumulation or transformation of pesticides), the way of receipt of substances to an organism, inclusion in metabolism and many other things. Given the complexity of the process of migration of toxic substances, mathematical models, such as empirical (statistical) and simulation are used for prediction of this process. Today, models such as LEACHP, PESTLA, MACRO, CALF, GLEAMS, CMLS, PRZM, PLEMO are used to predict the behavior of pesticides in agrobiocenoses. To evaluate the migration of pesticides in the ecosystem, a chamber model method can be used. It has shown its high efficiency in radioecology. This method is used to describe the migration of substances through trophic chains, which are divided into cells, and the transition between the cameras is determined by the coefficients of transition. By way of interaction between cameras, models are divided into stationary and dynamic ones. Для стаціонарних камерних моделей приймається, що концентрація речовини в кожній камері рівномірна, а між ними існує стала статистична рівновага. Для прикладу розглянута стаціонарна камерна модель, що характеризує трофічний ланцюг: грунт–рослина–тварина–людина. Концентрація  токсичної речовини в кожній камері ( С 1 , С 2 , С 3 , С 4 ), а перехід речовини  між камерами описується коефіцієнтом переходу (Кп і ), відповідно Кп 1 , Кп 2 , Кп 3 . For stationary chamber models it is assumed that the concentration of matter in each cell is uniform, and between them there is a statistical equilibrium. For an example, a stationary chamber model describing the trophic chain is considered: soil-plant-animal-man. The concentration of the toxic substance in each cell (C 1 , C 2 , C 3 , C 4 ), and the transition of matter between the cameras is described by the transfer coefficient, respectively, К t 1 , Кt 2 , Кt 3 . It is shown that the method of chamber models is a simple and adequate mathematical way of describing migration processes in ecosystems of varying complexity. It can be used, inter alia, for assessing migratory processes of pesticides in biocenoses. Conclusions . Given the need to reduce the environmental burden, the issue of studying the migration of pesticides in ecosystems is extremely relevant. To predict the migration of pesticides in biocenoses, mathematical models are widely used, in particular the method of chamber models, which is based on determining the coefficients of transition between cameras. The presented approach, based on the results of experimental (laboratory and field) studies, is possible for an adequate assessment of the ecological hazard of pesticides and the development of means to reduce their dangerous environmental impact.