Dispersion of radionuclides from coal-fired brick kilns and concomitant impact on human health and the environment

Highlights

• Coal fired brick kilns release terrestrial radionuclides via inhalable ash particles.

• •Prolonged inhalation of smoke/ash gives rise enhanced radiation exposure to lungs.

• •Hazardous level of absorbed dose and carcinogenic risk were found for exposed population

• •Respiratory protection of kiln workers and members of public is highly recommended for radioprotection reasons.

• This study suggests the discharging management of fly ash should be revised significantly.

Abstract

Realizing the probable health implications via the exposures to radionuclides released from coal-fired brick kilns, concentrations of terrestrial radionuclides in feed coal, fly- and bottom ash collected from some major coal-fired brick kilns of Southern region in Bangladesh were measured using HPGe γ-ray spectrometry. Respective mean activity concentrations (Bq kg⁻¹) for ²²⁶Ra, ²³²Th and ⁴⁰K were found to be 36.3 ± 1.8, 26.2 ± 2.1 and 314 ± 18 in feed coal; 60.8 ± 3.9, 36.6 ± 3.9 and 338 ± 19 in fly ash; 54.9 ± 4.0, 39.7 ± 4.6 and 311 ± 18.0 in bottom ash samples. As a result of the combustion process, radionuclide concentration enhancements have been observed in proceeding from feed coal to fly- and bottom-ash. The calculated values of air absorbed dose-rates for fly- and bottom-ash are greater than the world average of 55 nGy/h reported by UNSCEAR, and the Lifetime Cancer Risk (LCR) approaches towards the safe limit recommended by the ICRP. As such, this does flag up a potential concern for those dwelling in nearby areas, especially for the coal workers who normally do not take any protective measures against exposure to ash dust. Multivariate statistical analysis has been used in examining for correlations between the origins of the radionuclides and their influence on the calculated radiological parameters. The measured data indicate significance for human health, also for the scientific community, and could be used for modeling studies in the region.

Introduction

In Bangladesh, the construction of residential housing, educational and commercial complexes is increasing day-by-day, brick representing the most commonly used building material in the country. According to the Bangladesh Brick Manufacturing Owners Association, nationally approximately 6000 brickfields are responsible for the manufacturing of some 17 million bricks (per year) of different grades. According to the Department of Agricultural Extension, as many as 806 brick kilns are operational in the Chattogram division, 40 of them in the Rangunia Upazila of Chattogram district. Following a government regulation in 2013, more than 5000 brick kilns now use coal as the fuel. Coal is a sedimentary rock whose organic and inorganic mineral aggregates contain varying concentrations of naturally occurring radioactive materials (NORMs), including radionuclides in the uranium (²³⁸U) and thorium (²³²Th) decay chains and radioactive potassium (⁴⁰K) (Akkurt et al., 2009). During coal combustion, most of the ²³⁸U, ²³²Th, and their progeny are released from the original coal matrix and are distributed between the gas phase and solid combustion products. Virtually 100 percent of the radon gas (a progeny of ²³⁸U) that is present in feed coal is transferred to the gas phase, getting lost in stack emissions. In contrast, less volatile elements such as ²³⁸U, ²³²Th and the majority of their progeny are almost entirely retained in solid combustion waste. More specifically, during the combustion process, a coal-fired brick kiln produces two types of ash: fly- and bottom-ash. That which is carried along with the flue gas is called fly-ash, while the ash collected at the bottom of the boiler is known as bottom-ash. Depending on the emission control system of the stack, most of the fly-ash is recovered by the collection devices, any leftover that is released into the atmosphere being deposited on the soil around the coal-fired plants or kilns. In a coal-fired power plant, 80% of the ash content is released as fly-ash, into the atmosphere via the chimney, the remainder forming bottom ash (Hasan et al., 2014). Fly- and bottom-ash may also contain trace amounts of essential (mineral elements) and non-essential (toxic) materials.

The ash generated in the coal-fired brick kilns is generally used to fill low lying lands, this land later often going on to be used for agricultural purposes. Conversely, the ash from coal-fired brick kilns are mainly used in producing cement and other building materials or aggregate in stabilizing roadways. As a result, the combustion of coal redistributes the radionuclides in the soils and other dwelling compartments, thereby raising environmental radiation levels above normal background (Charro and Pena, 2013). After combustion, the mineral composition of coal may be absorbed by fine particulates that may suspend in the air environment or may deposit in the surrounding soil. These fine particulates can be directly inhaled by human beings, or otherwise indirectly affect human health through the food chain. The fly ash generated in coal-fired brick kilns has been linked to many life-threatening diseases, asthma and tuberculosis included. As an instance, black-lung diseases are prevalent among the so-called coal burners due to inhalation of coal dust in quantities that are beyond the capacity of cilia and other cleaning mechanisms of the lungs (Finkelman et al., 2002; Burt et al., 2013).

Realizing the health and environmental implications of radioactive-, trace- and toxic substances released during the coal combustion process, a good number of studies on the radioactive influence of coal-fired power plants to the ambient environment is available in the literature. However, data for feed coal and by-products from coal-fired brick kilns are scarce. Since a greater number of coal-fired brick kilns are in operation in many countries, including Bangladesh, and since the ashes produced may be either disposed-off or utilized further in other applications, it is thus important to perform a detailed study on radiation level in feed coal and its by-products. Furthermore, the bulk measurement of radionuclides concentration in by-products of combusted coal helps in developing more accurate estimation of radiation exposure both for those in associated occupations as well as to the general public. In this regard, the direct interest of present study is to determine the concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the feed coal, fly- and bottom-ash that are associated with major coal-fired brick kilns operating in the Southern region of Bangladesh. Several relevant radiological hazard parameters were calculated for health and environmental impact assessment given the scenario of radionuclides deposition in the surrounding soil and the use of kiln by-products as additives in building materials.