Assessment of environmental risk of water bodies in the conditions of mineral deposits development

A brief analysis of the mining industry impact on the environment is provided. It is proposed to assess the ecological situation of water bodies on the territory of Iron Ore Dressing Works (GOK) according to the magnitude of ecological risk (e.g. Iron Ore Dressing Works (Northern GOK)). Calculations of ecological risk values based on the content of microcomponents in the water were carried out for man-made (tailings storage) and natural water bodies (the Saksahan river, a pond in the Nedayvoda stream). It was concluded that over time (from 2014 to 2020) the ecological risk of most water bodies is increasing from 0.17 in the Saksahan river to -2.53 in tailings storage. The complex ecological situation on the territory of the Northern GOK proves the need to implement more effective environmental protection measures in order to achieve the criteria of sustainable development.


Introduction
The growth of humanity's needs set the global task of providing food with the necessary caloric content and composition, water of an acceptable quantity and quality, territory that provides many aspects of human activity, energy that does not cause global geo-ecological crises, and products of industrial activity that do not lead to an unacceptable level of environmental pollution.These needs are steadily growing, moving the ecosphere from a crisis, but still stable state to an unstable one and with further development of instability -to a global catastrophe.
The mining activity of the regions significantly affects their sustainable development.It can be a source of employment for local residents, a source of state income, an engine of economic growth and development of remote areas.However, significant environmental impacts and inequitable distribution of economic benefits can exacerbate instability and cause conflict.
Each problem of the mining industry is local, but the fundamental issues of mining in the relevant format are international in nature.Sustainable mining is a theoretical and highly unlikely goal to achieve.Metals and minerals are non-renewable resources, and their use can only be sustainable if consumption declines, and the rate of decline is going to be greater than the rate of depletion.From a practical perspective, achieving sustainability in the mining industry is a distant prospect, but many mining companies and industry associations are moving towards more economically, environmentally and socially responsible business practices.
Mining invariably benefits people and harms the environment.At the stages of their extraction and processing, numerous environmental problems arise.First of all, during the extraction and processing of minerals, a large geological cycle is disrupted, in which various systems are involved.As a result, there is a great impact on the ecology of the mining region, and such an impact has negative consequences.
Impact of mining on the lithosphere [1] 1.The development of deposits of dense rocks is accompanied by significant extraction of forested and agricultural lands.Mining leads to significant changes in the landscape: the creation of anthropogenic forms of meso-relief -quarries, dumps.2. Possible activation of geological processes (karst, landslides, scree, subsidence and displacement of rocks).During underground mining, subsidence pits and sinkholes are formed.3. Mechanical disturbance of soils and their chemical pollution.
Impact of mining on the atmosphere [1,2]: As a result of the processes of primary processing of mined ores, large volumes of mine methane, sulfur, and carbon are emitted into the air.In addition, a large amount of dust enters the air during mining.When 1,000 tons of explosives are used, about 40 million m 3 of atmospheric air is polluted, exceeding the limit of permissible concentrations tenfold, and its spread is possible over 15 km.As a result of mass explosions in quarries, from 0.027 to 0.170 kg of dust is formed per 1 m 3 of rock.
Every day, up to two kilograms of dust falls on the territory adjacent to the quarries, as a result, the soil remains buried under a half-meter layer for many years, and often forever, and, accordingly, loses its fertility.
It should also be noted the negative impact and composition of explosives used in open pit development.Harmful gases produced as a result of the explosion are released into the air for 10-15 hours [2].

Impact of mining on the hydrosphere
The development of mineral deposits by an open method causes not only the degradation of the earth's surface in the area of mining operations, but also a sharp change in hydrological and hydrogeological conditions, which lead to a change in the quality of surface and underground waters [1].As a result of the extraction of natural raw materials, reservoirs and underground waters are depleted, swamps are drained.
Surface waters suffer from pollution as a result of mineral extraction and processing.As in the atmosphere, a large amount of salts, metals, toxic substances, and wastes get into the water.As a result, microorganisms living in water bodies and fish die.If people use polluted water for their economic needs and for food, it leads to deterioration of the health of the population.

Methods
Assessment of the ecological situation of a certain region or the entire country is an urgent task today [3].Environmental risk has an important place in the environmental assessment of the current or projected situation.Environmental risk -at all levels: from local to globalassessment of the likelihood of negative changes in the environment caused by anthropogenic or other influences.It is important to note that any economic activity always has an environmental risk.
There are four main directions in risk assessment: engineering, modeling, expert and social.In the modeling direction, mathematical models of processes that lead to undesirable consequences for humans and the environment when using harmful chemicals and compounds are developed.
The theory of probability and the means of mathematical statistics are used for the quantitative analysis of environmental risk.A peculiarity of the assessment of environmental risks is their dynamism, that is, there is a need to monitor the state of the environment as a whole and its individual components.
For water bodies, ecological risk is the probability of undesirable consequences in water ecosystems and their components as a result of anthropogenic and natural factors, including a decrease in water quality.Several methods of ecological risk assessment have been developed and used both for individual regions and river basins, as well as for certain sections of rivers subject to anthropogenic pressure.
This study used the method of environmental risk assessment [4] according to the formulas: where: where: where C i is the concentration of the different pollutant (DP) that exceeds the threshold limit value (TLV) [5]; N is the total number of DP analyzed (content greater than TLV and less).

Results
The results of hydrochemical observations on the territory of the Northern GOK (Kryvyi Rih), which were conducted by the State Enterprise "Ukrchormetgeology", were used to assess the environmental risk.The water objects of the natural-technogenic complex of Northern GOK include the tailings storage facility and the section of the Saksahan river, ponds and man-made water objects (figure 1).
The Northern GOK tailings pond has been in operation since 1963.The main dam of the Northern GOK tailings pond is located at a distance of 2.5 km from the mouth of the Petrykov creek, which flows into the Saksahan River.Also, in Petrykov creek along the outer contour of the right-bank enclosing dam, tailings, two emergency tanks were created: the first -in the western part and the second -in the northern part of the tailings.The area of the tailings pond is 1295 ha (of which the tailings pond itself is 980.0 ha, the circulating water pond is 315.0 ha).The length of the tailings pond is 17.3 km (tailings pond -11.0 km, circulating water pond -6.3 km).The contour of the tailings pond is closed by a 1.2 km long dividing dam, which separates the circulating water supply pond from the tailings pond itself.In addition to sludge pulp, quarry water (2.5 million m 3 / year), mineralization mine water (5.5 million m 3 / year), wastewater from treatment plants (36.15 thousand m 3 / year), and precipitation are discharged into the tailings pond, and surface filtration waters that were made from drainage systems built around the storage [6].
Preliminary studies have established that a persistent geochemical and hydrochemical anomalies has formed on the territory of the Northern GOK.
The center of the anomalies is a tailings, which pond's water has an elevated content of microcomponents: lead, cadmium, vanadium, bromine [6].
The content of some microcomponents also has an increased in the water of the river Saksahan and in the water of the pond Nedayvoda.
The results of the ecological risk calculations of water bodies on the territory of the Northern GOK are presented in figure 2. According to the results of the calculations, it can be concluded that in general the ecological situation in the water bodies of the Northern GOK is deteriorating.The greatest concern is the too high content of bromine, both in the water of the tailings pond and in the water of water bodies.Let me remind you that bromine belongs to the second class of danger [5].Bromine is a chemical element that is energetically accumulated by plants, animals in landscapes [7].An excess of bromine in the human body leads to a decrease in the concentration of iodine in the hormones of the thyroid gland (hyperthyroidism), and also contributes to the rapid release of chloride ions by the kidneys.
The main symptoms of excess bromine are: memory impairment, insomnia, skin rashes, indigestion, bronchitis, rhinitis, as well as possible neurological disorders.Since this trace element is considered a very poisonous substance, the ingestion of a large amount of it into the human body causes serious consequences, even fatal.[8] As mentioned earlier [6], the main source of bromine in the tailings pond is mine water.Among the heavy metals, an increased content of lead and vanadium is always noted, which enter the water of the tailings pond and the water of surface water bodies from the enrichment tails.
Among the studied natural and man-made water bodies, the greatest ecological risk is noted in the tailings stogare (-2.  in environmental risk values over time do not have a clear dependence.This is due to the fact that the hydrochemical regime of the river is formed under the influence of not only man-made but also natural factors.
It should also be noted that information for assessing the environmental situation in Kryvbas is not publicly available.This is also noted in the report [9,10] and is a significant drawback of mining and blasting enterprises.Thus, the Metinvest company received zero marks for the Hannivskyi and Pervotravnev quarries, as it did not provide evidence to verify the information or did not provide information at all.Therefore, in order to achieve world standards in the field of mineral extraction according to the criteria of sustainable development, Ukrainian companies still need to pay a lot of attention to the issues of openness of information about nature protection in all main directions: protection and rational use of land, atmosphere, water resources, subsoil, managing of production waste.

Conclusions
The mining industry has a significant effect on the ecological state of water bodies, which is confirmed by the calculated value of ecological risk.It was determined that the water of the tailings storage has the greatest environmental risk (-2.53 on 05/04/2020), the Saksagan River (0.17 on 03/19/2014) has the lowest.The magnitude of ecological risk increases over time in almost all water bodies.The proposed method of calculating environmental risk for water bodies can be used to analyze the effectiveness of environmental protection measures and sustainable development of mining areas.

Figure 1 .
Figure 1.Map of Northern Iron Ore Dressing Works in Kryvbas with observation points for chemical composition of water (downstream) № 1 -Tailings dam NorthernIron Ore Dressing Works; № 2 -the first water meter post, the Saksahan River; № 3 -the second water meter post, the Saksahan River; № 4 -pond in the beam Nedaivoda.
53) as of 05/04/2020.It should be noted that over time the ecological risk increases in the tailings stogare and in the pond Nedayvoda.In the Saksahan River, changes -date 19.03.2014 -date 18.05.2015-date 04.05.2020

Figure 2 .
Figure 2. Environmental risk schedule for water bodies on the territory of the Northern GOK by observation points: 1 -Tailings dam Northern Iron Ore Dressing Works; 2 -the first water meter post, the Saksahan River; 3 -the second water meter post, the Saksahan River; 4 -pond in the beam Nedaivoda (2014, 2015, 2020).