Ekologia

CARCINOGENIC RISK OF ZIRCONIUM INDUSTRY OF UKRAINE

Doctor Levenets V.V., doctor Neklyudov I.M., Rolik I.L.

National Science Center “Kharkov Institute of Physics and Technology”

61108, Kharkov, Ukraine, 1, Academicheskaya Str.

levenets@kipt.kharkov.ua; rolik@kipt.kharkov.ua

Abstract. Article is dedicated to scientific problem which is assessing the impact of zirconium production companies of the nuclear power industry of Ukraine on ecological safety and humans using principles of ecological risk assessment methodology for humans. Under influence of State Scientific and Production Enterprise “Zirconium” outliers the evaluation of carcinogenic risk for health of Dneprodzerzhinsk city population has been carried out. A map-scheme of the spatial distribution levels of carcinogenic risks at the location of enterprise was developed. It was found that the determining factor for an unacceptable level of environmental risk in Dneprodzerzhinsk is a background pollution. The determining factor for an unacceptable risk level on the territory of industrious site SSPE “Zirconium” is joint effect of background pollution and emissions of the enterprise.

Key words: zirconium production, nuclear fuel, ecological safety, carcinogenic risk assessment, air pollution.

I. Introduction

State Scientific and Production Enterprise “Zirconium” (SSPE “Zirconium”) is one of the main parts of the nuclear-pure zirconium alloy production in Ukraine. The enterprise is located in Dneprodzerzhinsk, Dnepropetrovsk region, which is one of the main centers of ferrous metallurgy, chemical and chemical-recovery industry of Ukraine. With population of 276 thousand people 1.75% of the country’s products are produced here, i.e. the load three times higher the average. As a consequence, the peculiarity of the city is high urbanization and unfavorable ecological situation which reflects directly on the health status of the city. The acute cancer problem: sickness rate is 37.27 per 10 thousand of population average during the years 2002-2006, death-rate from malignant tumors is 25.44.

The objective of this work is to study the impact of atmospheric emissions from SSPE “Zirconium” on the level of cancer rates of Dneprodzerzhinsk population.

Relevance of these studies is determined by the prospects of increasing the capacities of zirconium production according to the Energy Strategy of Ukraine till 2010 [1] as well as lack of information on potential contribution of SSPE “Zirconium” in the formation of general background cancer rates in the city.

II. Methods of research

To achieve this objective we used the principles of methodology for assessing the carcinogenic risk [2, 3] carried out in four stages:

1. Risk identification.

2. Impact assessment.

3. Assessment of dose-response relationship.

4. Risk characteristics.

Risk identification is carried out based on ecological characteristics of the studied production and territory of its impact [4]. As a result, atmospheric emissions were selected as the main negative factor of SSPE “Zirconium” that has a direct impact on human health. Population that lives in the area of the enterprise influence and workers of the industrial area of SSPE “Zirconium” are the potentially exposed groups. Chrome and carbon were selected as priority pollutants as among the substances present in plant emissions only they possess carcinogenic effect [5].

Selection of preliminary scenario and route of chemicals exposure (table 1) was done based on the obtained information.

Table 1.

Exposure scenario

Source of pollutants	Atmospheric emissions of enterprise from stationary organized sources
Inflow route	Inhalation
Impact scenario	Residential area				Industrious area
Type of impact on the time of contact	Acute	Lifetime (70 years)			Acute	Chronic (30 years)
Age of the exposed group	Average person	≤ 6	6-18	18≥	18≥	18≥

Impact assessment was to calculate specific doses of receipt of pollutants in the human body [2,3]:

, (1)

Where ADDi – average daily rate of i-substance and mg/kg of body weight per day;

Ci – average annual concentration in receptor point of i-substance, mg/m³;

CR – respiration rate, m³/hour;

EF – effect frequency, number of days/year;

ED – effect duration, number of years;

BW – body weight: average body weight during exposition, kg;

AT – exposure averaging period, number of days.

Lifetime daily dose considering age periods (LADD) was calculated as average dose for three life periods using the following formula [2]:

, (2)

Where LADD – lifetime average daily dose, mg/kg of body weight per day;

EDb – duration of exposure for younger children (< 6 years);

EDc – duration of exposure for older children (6-18 years);

EDa – duration of exposure for adults (> 18 years);

ADDchb – chronic average daily dose for younger children, mg/(kg-day);

ADDchc – chronic average daily dose for older children, mg/(kg-day);

ADDcha – chronic average daily dose for adults, mg/(kg-day);

AT – averaging time, number of years (70).

Three types of variables were used to calculate the intake:

1) Describing the exposing population – value of the contact, frequency and duration of effect, body weight (table 2);

2) Determined by researcher – time of exposure averaging, depends on type of assessed toxic effects (table 2);

3) Related to chemical substance – concentration influence.

Table 2.

Characteristics of exposure

Parameter	Characteristics	Standard value
CR	Respiration rate, m^3/hour	children under 6 years – 4; children from 6 to 18 лет – 20; adults from 18 лет – 22; average person - 20
EF	Effect frequency, days/year	сценарий селитебный – 350; сценарий промышленный - 83
EDi	Effect duration, years	Lifetime: - children under 6 years - 6; - children from 6 to 18 years -12; - adults from 18 years - 52; Chronic – 30; Acute - (EF × ED =1)
BW	Body weight, kg	children under 6 years - 15 children from 6 to 18 years - 42 adults from 18 years - 70 average person - 60
AT	Period of exposure averaging, days	carcinogens - 365×70;

Affecting concentrations were evaluated on the basis of dispersion simulation of pollutants from stationary sources of pollution of SSPE “Zirconium” which was carried out using computer program Eol-Plus 5.23. This approach allowed to determine the affecting concentrations with and without consideration of background of contaminants in the affected area.

As the simulation results provide maximum annual concentrations of pollutants, to obtain average annual data we used information that, as a rule, maximum one-time, average daily, monthly and annual average concentrations are correlated as 10 : 4 : 1,5 : 1, i.e., average annual concentration is usually one order less than maximum [6]. Maximum annual concentrations were used in calculations the risks of acute effects, average annual-chronic.

In assessment of dose-response relationship the so-called linear threshold model of carcinogenesis was used according to which the exposure even of a small quantity of substance in theory gives a finite increase of cancer risk. This model was implemented using the so-called factors of carcinogenic potential and as a result was brought to obtaining the value of lifetime risk.

Carcinogenic potential factor (CPS) or “slope factor” (SF) (mg/kg-day)^-1 is a risk per unit dose of this substance. It is determined by splitting the risk at the highest level on the dose [2].

The risk of an individual over a lifetime or the lifetime risk (Rind) – is excess (increase) of probability that during the lifetime there will be some disturbances as a result of influence on the agent’s risk. It is determined as an extra in comparison with the background risk for individual to have cancer in the lifetime when exposed to specific substances in certain concentration or dose:

Rind = ADD_i · CPS, (3)

Where Rind is the risk of an individual during the lifetime;

ADD_i – average daily dose of i-substance intake, mg/kg of body weight per day;

CPS – is a factor of carcinogenic potential (mg/kg-day)^-1. Acceptability of the obtained values was given in accordance with the generally accepted criteria system recommended by WHO [2].

Calculation of carcinogenic risks according the above described methodology was done in computer program EcoAir [7]. Spatial data analysis and mapping of risk level distribution was done in GIS ArcView 3.2a.

Use of carcinogenic risk assessment method allows to calculate risk on the highest (95%) confidential limit of risk assessment under assumption of certain reassessment of risk. The value of this risk should not be used to conduct direct similarities between the levels of actual cancer rates or death-rates, and values of these risks. Mainly, they reflect a long-term tendency to change the cancer background which is formed under the influence of risk factors.

III. Results of research

III.I. Characteristics of influence area

SSPE “Zirconium” implements and hydro metallurgical concentrate to produce zirconium ingots of CTC alloy. The enterprise is located on the right bank of the Dnieper river in the industrious North-Eastern part of Dneprodzerzhinsk city, Dnepropetrovsk region, its sites are near and mixed with workshops of other more powerful metallurgical and chemical productions (Closed joint-stock company “DZMU”, SE “PGMZ”, “DneprAzot Ltd.” etc) (fig. 1).

Note: hereinafter:

Fig. 1. Schematic map of SSPE “Zirconium” location

General status of biosphere elements in the studied region is characterized in table 3.

General technological scheme for production of ingots from zirconium alloys is represented by following stages [10]:

· Sintering of zirconium concentrate with technical sodium hydroxide (granular);

· Cake washing from excess alkali alkali silicon;

· Desiliconization of alkaline solutions;

· Nitrate leaching of hydrated zirconium cake;

· Extraction separation of zirconium and hafnium;

· Hafnium hydroxide obtaining by ammonia precipitation with its further transfer to pilot production;

· Evaporation of zirconium re-extract;

· Precipitation of zirconium tetrafluoride monohydrate (ZTM)∙40% by hydrofluoric acid;

· Drying, dehydration of ZTM monohydrate and desorption of fluoride hydrogen;

· Sublimation purification of ZTM from impurities;

· Calcium and thermal reduction of ZTM to produce bullion ingot of zirconium;

· Refining re-melting of bullion ingot to obtain KTC-110 ingot;

· Mechanical processing of ingot.

Table 3.

Indices of biosphere elements pollution in Dneprodzerzhinsk city [8, 9]

The environment object	Pollution indices	Pollution category	Indices and properties according to which the calculation was done
Atmospheric air	250-365	extremely high	main and specific pollutants
Surface water	5-12	moderate	organoleptic, toxicological properties and health regime
Soil	3-4	increased	average doses in the state for all pesticides considering their disintoxication

III.II. Risk characteristics

III.II.I. Scenario of residential area.

Calculation results of carcinogenic risks indicate that risk values are at minimum acceptable level (with and without background contamination) (see table 4) under acute exposure of chromium and soot on population.

Table 4

Carcinogenic risk for population

Substances	Background	Without background				With background
		On all studied area				On all studied area
		min	max	mean	σ	min	max	mean	σ
Rind ac
Chromium	3E-07	0	3E-07	4E-08	9E-08	0	4E-07	4.3E-07	6E-08
Soot	0	0	0	0	0	0	0	0	0
∑	3E-07	0	3E-07	4E-08	9E-08	0	4E-07	4.3E-07	6E-08
Rind ch
Chromium	8E-04	5.5E-05	8E-04	7E-05	6E-05	8E-04	0.002	9E-04	6E-05
Soot	3E-05	8E-08	1E-07	1E-07	4E-08	3E-05	3E-05	3E-05	0
∑	8E-04	5.5E-05	8E-04	7E-05	6E-05	9E-04	0.002	9E-04	6E-05

Values of carcinogenic risks in the residential area in lifelong impact of emissions directly from SSPE “Zirconium” (without background) are at low and minimum risk level for chromium and soot, respectively. Registration of background results in increase of individual risk values to medium (unacceptable) level for chromium and low level for soot (see table 4, fig. 2, 3). Herewith, risks at chromium background concentration are unacceptable, and risk values for soot are determined completely by background contamination.

Note: hereinafter:

Fig. 2. Spatial distribution of carcinogenic risk values for population health at lifelong chromium impact: a). without background; b). with background.

Fig. 3. Space distribution of carcinogenic risk values for population health at lifelong soot impact: a). without background; b). with background.

Values of total carcinogenic risk indicate that maximum number of people for which emissions SSPE “Zirconium” contribute to the formation of malignant tumors of <1 in 10 thousand, and for background noise, this value ≈ 8 to 10 thousand (see table 4, fig. 4). Difference in absolute risk values between chromium and soot leads to the fact that the overall risk of 97% determined by the influence of chromium.

Fig. 4. Spatial distribution of total values for carcinogenic risks for population health at lifelong impact: a). without background; b). with background.

III.II.II. Scenario of working area.

Carcinogenic risks observed at acute exposure of chromium and soot on population are one order or more lower than acceptable ones (table 5).

Table 5.

Carcinogenic risk for workers

Substances	Back-ground	Without background				With background
		On all studied area				On all studied area
		min	max	mean	σ	min	max	mean	σ
Rind acw
Chromium	3E-07	0	0	0	0	3E-07	6E-07	3.4E-07	9E-08
Soot	0	0	0	0	0	0	0	0	0
∑	3E-07	0	0	0	0	3E-07	6E-07	3.4E-07	9E-08
Rind chw
Chromium	8E-05	5E-06	7E-05	7E-06	6E-06	8.2E-05	1.5E-04	8E-05	6E-06
Soot	3E-06	0	0	0	0	2.9E-06	3E-06	3E-06	0
∑	8E-05	5E-06	7E-05	7E-06	6E-06	9.1E-05	1.6E-04	9.2E-05	6E-06

Level of carcinogenic risk at acute exposure on workers is at minimum level for soot, with and without background contamination (table 5). All studied area with chromium exposure (with and without background) is characterized by low risk level, and only background registration results in average (acceptable for workers) risk level on Eastern part of industrial site (fig. 5). Herewith, background risks in themselves are higher than maximum risks caused by emissions impact, though they are on a low level.

Note: hereinafter:

Fig. 5. Spatial distribution of carcinogenic risk values for health of workers at chronic exposure of chromium: a). with background; b). without background.

Values of total carcinogenic risk indicate that maximum number of workers for whom emissions from SSPE “Zirconium” contribute to the formation of malignant tumors makes ≈ 0.7∙ per 10 thousand, herewith, for background contamination this value makes ≈ 0.8 per 10 thousand (table 5, fig. 6). Total carcinogenic risk is almost (98%) determined by chromium exposure as well as in scenario for residential area.

Fig. 6. Spatial distribution of total carcinogenic risk values for health of workers at chronic exposure: a). without background; b). with background.

IV. Conclusions

Assessment of emissions impact from SSPE “Zirconium” has been carried out into formation of cancer rates for population of Dneprodzerzhinsk. Calculations of carcinogenic risks for the health of population that lives in the area of enterprise impact and people that work in the industrial area of this enterprise with acute and chronic effect.

It is determined that level of cancer risk with direct impact from SSPE “Zirconium” emissions is at acceptable level for population as well as for workers and makes <1 and 0.7 per 10 thousand, respectively. Registration of background results in increase of data indices up to 10 and 106 per 10 thousand whish is unacceptable for population and acceptable for conditions of the working area. Due to background contamination, the level of cancer rate, herewith, for population is formed on 85% and for workers on 55%. The obtained values of carcinogenic risks are determined by effect from chromium and soot with the share of chromium equal to ≈ 97% of contribution.

Therefore, SSPE “Zirconium” contribution into formation of cancer rate level for population and workers is acceptable and is at essentially lower level than contribution of background contamination of atmosphere.

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