Phosphogypsum and its potential use in Croatia: challenges and opportunities.

Phosphogypsum (PG) is a waste by-product (residue) originating from the production of phosphoric acid and phosphate fertilisers. PG contains chemical and radioactive impurities, which is why it is mostly stockpiled in controlled areas. Worldwide, only about 15 % of PG is recycled or reused. Today, policies and business strategies prioritise sustainable development through circular economy, which certainly includes PG. This provides new opportunities for Croatia to manage its PG and make an effort to use it as an additive in different industries, such as agriculture and construction. Due to its chemical and radiological properties, PG can potentially cause problems for the environment and human health. Hence, before using PG, detailed knowledge of potential hazards is necessary to protect people and the environment. The aim of this review is to summarise available data on Croatian PG, compare them with other countries, and to identify knowledge gaps and the lack of data on potential hazardous substances in PG in order to assess the opportunities of using PG in Croatia.

Radioactivity of soil in Croatia I: naturally occurring decay chains.

The assessment of environmental radioactivity much relies on radionuclide content in soil. This stems from the significant contribution of soil to both external and internal exposure to ionising radiation via direct emission of gamma radiation and soil-to-plant radionuclide transfer, respectively. This motivated us to carry out a systematic research on the radioactivity of soil in Croatia to obtain relevant data that can be used as a basis for understanding the related effects of geomorphological, biogeographical, and climatological properties of the environment. We collected samples of the surface layer of uncultivated soil (0-10 cm) at 138 sites from all over the country and measured them for radionuclide activity concentrations by means of high-resolution gamma-ray spectrometry. This resulted in radioactivity maps containing data on activity concentrations of representative radionuclides in the environment. In this paper, which is the first in our two-part presentation, we focus on the naturally occurring 232Th and 238U decay chains and their correlations with the diversity of Croatian regions. For both of the chains, activity concentrations were the highest in the Dinaric region, the lowest in the Pannonian region, and intermediate in the Adriatic region. Relatively high concentrations of 226Ra in the soil of the Dinaric region implied a possibility of an enhanced emanation of its progeny 222Rn into the air. Activity concentrations of 210Pb were additionally elevated in areas with dense vegetation, most probably due to an atmospheric deposition of airborne 210Pb onto the surface of plants and their eventual decomposition on the ground.

Radioactivity of soil in Croatia II: 137Cs, 40K, and absorbed dose rate.

We took samples of uncultivated soil from the surface layer (0-10 cm) at 138 sites from all over Croatia and measured their radionuclide activity concentrations with high-resolution gamma-ray spectrometry. This second part of our report brings the results on 40K and 137Cs to complement those on the 232Th and 238U decay chains addressed in the first part. Together they give the most complete picture of radioactivity of Croatian soil so far. Activity concentrations of 40K were the highest in the Pannonian region, and there was an opposite trend for 137Cs. We found that the concentrations of 137Cs tended to increase with altitude, annual precipitation, and vegetation density. The concentration ratio of 137Cs and K in soil, which indicates the potential for 137Cs entering food chains via uptake by plants, was the lowest in agriculturally important areas in the east of the Pannonian region. In addition, we used the obtained results on activity concentrations to calculate the related absorbed dose rate as a measure of external exposure to ionising radiation from soil. The sum of the absorbed dose rates for naturally occurring radionuclides and 137Cs showed that external exposure was generally the highest in the Dinaric region and Istrian Peninsula.

Distribution and transfer of naturally occurring radionuclides and 137Cs in the freshwater system of the Plitvice Lakes, Croatia, and related dose assessment to wildlife by ERICA Tool.

The aim of this study was to investigate the natural radioactivity of Plitvice Lakes, under the assumption that due to its status as a National Park, the area can be considered an example of a natural freshwater system. Also, considering the transfer parameter data as the largest source of uncertainty in radiological risk assessments, the impact of site-specific data on dose rate assessment, as opposed to currently available data, was investigated. The study included gamma and alpha spectrometric measurements of 238U, 226Ra, 210Pb, 228Ra, and 40K in water, sediment, and fish samples, as well as 137Cs due to the coinciding of the study with the Fukushima accident. The content of naturally occurring radionuclides significantly varied in sediments of different Lakes, probably as a reflection of the different underlying geology of the area. Also, the 210Pb distribution in sediments indicated an up to 312 Bq kg-1 of the allochthonous contribution of this radionuclide at the beginning of the Lake's watercourse, which probably entered into the lake system by the major inlet river with its steady decrease along downstream lakes. Low 40K activity concentrations (27.5 ± 20.1 mBq L-1) in the Lake's waters might be one of the causes of increased 137Cs activity concentrations in fish samples (1.5 ± 0.4 Bq kg-1), which was found to be an order of magnitude higher than average values for different fish species from other Croatian freshwater systems (0.2 ± 0.1 Bq kg-1). A temporary increase of 137Cs activity concentrations was measured in water samples collected immediately after the Fukushima accident. Calculated site-specific sediment/water distribution coefficients and fish/water concentration ratios for radium and caesium were on average lower than generic ones found in the literature. Background dose rate assessments performed by the ERICA Tool indicated a profound impact of different input data on assessment results with water activity concentrations resulting in significantly higher dose rates (0.1-67 µGy h-1) in comparison to sediment activity concentrations (0.03-9 µGy h-1). An incremental dose rate due to 137Cs was found to be in the range of < 0.001-0.023 µGy h-1 which, in comparison to background dose rates, can be considered negligible.

Baseline radioecological data for the soil and selected bioindicator organisms in the temperate forest of Plitvice Lakes National Park, Croatia.

The aim of this study was to provide baseline radioecological data for the temperate forest ecosystem in Plitvice Lakes National Park. Emphasis was placed on the determination of naturally occurring radionuclides since there is an acknowledged lack of data for these radionuclides in non-accident conditions in wildlife, even for bioindicator organisms. Activity concentrations of 238U, 226Ra, 210Pb, 232Th, 40K, 134Cs, and 137Cs were measured by gamma spectrometry in soil and bioindicators: earthworms, conifer needles, mosses, and lichens. From the measured activity concentrations, concentration ratios were calculated to quantify the transfer of these radionuclides from soil to bioindicators. Our results show that soil activity concentrations are biased toward results from other studies conducted within the Dinaric mountain region. However, in moss and lichen samples, we measured higher activity concentrations of 226Ra and lower activity concentrations of 40K and 137Cs in comparison to similar studies. Also, we estimated lower concentration ratios for all radionuclides from soil to these organisms, except for 210Pb, in comparison to generic values. The transfer of 238U was generally low for all of the bioindicator organisms. For conifer needles, a correlation was found between activity concentrations of 226Ra and 137Cs in soil and related concentration ratios. Correlation was also found between the activity concentration of 40K in soil and transfer of 40K and 137Cs to mosses and lichens. A comparison with literature data highlighted the lack of 226Ra related concentration ratios for conifer trees and especially for earthworms. Therefore, the results of this study could supplement the sparse data currently available on radionuclide background data in similar ecosystems and related soil-to-wildlife transfer of radionuclides. Dose rate assessments, performed by the ERICA Tool, estimated that 96% of the overall exposure of wildlife in the Park area is due to the background dose rates, while 0.06 µGy h-1 on average can be attributed as an incremental dose rate from 134Cs and 137Cs.

Experiences with the accreditation of the Institute for Medical Research and Occupational Health, Zagreb, Croatia.

Accreditation in accordance with the international General Requirements for the Competence of Testing and Calibration Laboratories (HRN EN ISO/IEC 17025 standard) has become a widely accepted method of quality management and objective evidence of technical competence, knowledge, and skills of testing and calibration laboratories. In 2010, the Institute for Medical Research and Occupational Health (IMROH) had its management system accredited against the HRN EN ISO/IEC 17025 standard for the following scopes: determination of radioactivity, testing of ambient air quality, and testing in the scope of ionising radiation protection. This accreditation encompassed three laboratories: Radiation Protection Unit, Environmental Hygiene Unit, and the Radiation Dosimetry and Radiobiology Unit. In accordance with the rules of the Croatian Accreditation Agency, the second re-accreditation is due in 2020. This paper describes and discusses the quality management system at IMROH over the ten years of its implementation. We share our experiences about non-conformities discovered during regular work, internal audits, and external audits performed by the Croatian Accreditation Agency. The accredited management system significantly improved the performance of the accredited units, and the Institute increased its visibility and marketing advantage, consequently improving its market position.

Assessment of multiple anthropogenic contaminants and their potential genotoxicity in the aquatic environment of Plitvice Lakes National Park, Croatia.

In this study, the influence of anthropogenic pollution on the aquatic environment of Plitvice Lakes National Park (PLNP) was investigated during 2011-2012 using a combination of chemical and cytogenetic analyses. Four groups of major contaminants [(volatile organic compounds: benzene, toluene, ethylbenzene, and xylenes (BTEX); persistent organochlorine pollutants: organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs); major and trace elements; anthropogenic radionuclides (90Sr, 134Cs, and 137Cs)] were determined in three aquatic compartments (water, sediment, fish). Mass fractions of inorganic constituents in different compartments reflected the geological background of the area, indicating their origin from predominantly natural sources. Levels of volatile and persistent organic compounds in water and fish, respectively, were very low, at levels typical for remote pristine areas. Analysis of anthropogenic radionuclides in water and sediment revealed elevated activity concentrations of 137Cs in water, and measurable 134Cs in the upper sediment layers from April 2011, possibly as a consequence of the Fukushima nuclear accident in March 2011. The potential genotoxicity of river and lake water and lake sediment was assessed under laboratory conditions using the alkaline comet assay on human peripheral blood lymphocytes, and measured levels of primary DNA damage were within acceptable boundaries. The results showed that despite the protected status of the park, anthropogenic impact exists in both its terrestrial and aquatic components. Although contaminant levels were low, further monitoring is recommended to make sure that they will not rise and cause potentially hazardous anthropogenic impacts.

RADIONUCLIDE AND MAJOR ELEMENT ANALYSIS OF THERMAL AND MINERAL WATERS IN CROATIA WITH A RELATED DOSE ASSESSMENT.

Major elements concentrations (Na, K, Ca, Mg) and the activity concentrations of 226,228Ra, 234,238U, 210Po, 210Pb, 40K and 137Cs in northern and eastern Croatian thermal and mineral waters, collected directly from springs (or wells), are presented herein with total effective doses assessed for those waters that are considered as drinking 'cures' and are available for consumption. The methods used for radionuclide determination included alpha-particle spectrometry, gas-proportional counting and gamma-ray spectrometry, while the major element composition was determined by ICP-MS. The activity concentrations of all of the radionuclides were found to be below the guidance levels set by the WHO and EC Directive, with the exception of one water sample that measured 0.26 Bq L-1 of 228Ra. The effective ingestion dose assessment for the consumption of the so-called water 'cures' during 1, 2 or 4 weeks' time period throughout 1 year was well below the recommended 0.1 mSv for drinking water.

Toxic airborne S, PAH, and trace element legacy of the superhigh-organic-sulphur Rasa coal combustion: Cytotoxicity and genotoxicity assessment of soil and ash.

This paper presents the levels of sulphur, polycyclic aromatic hydrocarbons (PAHs), and potentially toxic trace elements in soils surrounding the Plomin coal-fired power plant (Croatia). It used domestic superhigh-organic-sulphur Rasa coal from 1970 until 2000. Rasa coal was characterised by exceptionally high values of S, up to 14%, making the downwind southwest (SW) area surrounding the power plant a significant hotspot. The analytical results show that the SW soil locations are severely polluted with S (up to 4%), and PAHs (up to 13,535ng/g), while moderately with Se (up to 6.8mg/kg), and Cd (up to 4.7mg/kg). The composition and distribution pattern of PAHs in the polluted soils indicate that their main source could be airborne unburnt coal particles. The atmospheric dispersion processes of SO2 and ash particles have influenced the composition and distribution patterns of sulphur and potentially toxic trace elements in studied soils, respectively. A possible adverse impact of analysed soil on the local karstic environment was evaluated by cytotoxic and genotoxic methods. The cytotoxicity effects of soil and ash water extracts on the channel catfish ovary (CCO) cell line were found to be statistically significant in the case of the most polluted soil and ash samples. However, the primary DNA-damaging potential of the most polluted soil samples on the CCO cells was found to be within acceptable boundaries.

The impact of multiple anthropogenic contaminants on the terrestrial environment of the Plitvice Lakes National Park, Croatia.

The anthropogenic impact on the terrestrial environment of the Plitvice Lakes National Park (PLNP) was investigated through the analysis of three groups of major contaminants (persistent organochlorine pollutants including 15 organochlorine pesticides (OCPs) and 17 polychlorinated biphenyls (PCBs), trace elements/heavy metals (6 major and 23 trace constituents), and anthropogenic radionuclides ((90)Sr, (134)Cs, and (137)Cs)) in three terrestrial compartments (soil, air, and bioindicators of air contamination) during 2011-2013. The correlation coefficients of element mass fractions with soil properties indicated that total Fe and Al minerals, soil organic matter (OM), and organic carbon (OC) content affected the mass fractions of most trace elements in the topsoils. The annual and spatial distributions of heavy metals in total deposited matter (TDM) indicated that the metals came from natural sources and long-range transfer of particulate matter. The PCB and OCP levels found in soil and conifer needles corresponded to global environmental pollution levels by persistent organic pollutants and represented the lower end of the mass fraction ranges reported in the relevant literature. Analyses of anthropogenic radionuclides in bioindicators (conifer needles, lichens, and mosses) showed low but measurable activity concentrations of (134)Cs (for the first time after the Chernobyl accident), which indicated origin from the March 2011 Fukushima Nuclear Power Plant accident. Our overall results indicated that human activity inside or near the PLNP had no significant impact either on contaminant spread by air or on their content in topsoils.

Measuring and modelling the radiological impact of a phosphogypsum deposition site on the surrounding environment.

Phosphogypsum (PG) is a waste product (residue) from the production of phosphoric acid characterized by technologically enhanced natural radioactivity. Croatia's largest PG deposition site is situated at the edge of Lonjsko Polje Nature Park, a sensitive ecosystem possibly endangered by PG particles. This field study investigates two aspects relevant for the general radiological impact of PG: risk assessment for the environment and risk assessment for occupationally exposed workers and local inhabitants. Activity concentrations of natural radionuclides ((238)U, (235)U, (232)Th, (226)Ra, (210)Pb, and (40)K) were measured in the PG (at the deposition site), soil, and grass samples (in the vicinity of the site). The ERICA Assessment Tool was used to estimate the radiological impact of PG particles on non-human biota of the Lonjsko Polje Nature Park. The average annual effective dose for occupationally exposed workers was 0.4 mSv which was within the worldwide range.

A new approach to determine the phosphogypsum spread from the deposition site into the environment.

Phosphogypsum (PG), a waste product in phosphate fertilizer production, is characterized by technically enhanced natural radioactivity. The presented investigation was performed on a PG deposition site in Croatia. A new approach in the determination of the spread of PG particles from the deposition site into the environment based on the PG particle radioactivity measurements is suggested and explained. The stationary diffusion model was assumed and employed to describe long term PG particle transfer into the surroundings. The advantage of this method is that it requires a minimal number of measurement locations and offers a realistic and reliable distribution of PG particles. The mass concentration of PG particles decreased to the distance of about 3m, at most up to 10 m from the deposition site edge. The results indicate that a unique mechanism of particle transport exists and the migration of PG particles by surface water is the dominant way of their spread. The particle current deduced from the measurements was very low, approximately 4.05 × 10(-2)kg/h, and the migration coefficient was approximately 1.69 × 10(-5)m(2)/h. The obtained results confirmed the initial hypothesis of the stationarity of the migration process, reached within about 6 years.

Quality assurance in gamma-ray spectrometry of seabed sediments.

This article brings the results of a method for quality assurance in gamma-ray spectrometry of seabed sediments. Sediments were collected in selected locations of the South and Middle Adriatic Sea using grab and corer tools. Using our own experimental design, we determined the self-attenuation factors of selected samples. The article also discusses sources of uncertainty in gamma-ray spectrometry, which is another important issue in quality assurance. Together with self-attenuation correction sources of uncertainty are used to calculate the activity concentration for a given sample. The presented procedure demonstrates how a gamma-ray spectrometry experiment should be approached in order to properly account for errors and uncertainties specific to a particular sample.

Gamma radiation and dose rate investigations on the Adriatic islands of magmatic origin.

Natural radioactivity of Middle-Adriatic Sea islands and islets was measured. Gamma spectrometric measurements, both in situ and in laboratory, as well as radon measurements in the seawater were performed. Activity concentrations and the associated dose rates due to naturally occurring (232)Th, (238)U and (40)K radioisotopes were determined. Dose rates calculated from in situ gamma spectrometry are in correlation with dose rates calculated from activity concentrations measured in collected samples of pebbles and rocks. In situ gamma ray spectrometry in the seawater has been performed, showing activity concentration of 220 and 240 Bq m(-3) for (214)Bi and (214)Pb, respectively due to the presence of magmatic rocks in the seabed. The radium equivalent activity varied from 13 to 53 Bq kg(-1). These values are lower than the limit values, indicating that the radiation hazard is not significant. The highest mean activity concentrations of naturally occurring radionuclides in rock samples collected were found on the islands of magmatic origin.

Natural radioactivity of 226Ra and 228Ra in thermal and mineral waters in Croatia.

Thermal waters are known as valuable natural resources of a country. They contain certain degree of natural radioactivity attributable to the elements of the uranium and thorium natural decay series. Among these elements, the most radiotoxic and the most important is radium that exists in several isotopic forms (226Ra and 228Ra). The focus of attention was the content of radium in samples of thermal and mineral spring water from several spas in Croatia. These waters are mainly used for medical, bathing and recreational purposes, and some of them are used for drinking. Measured activity concentrations of 226Ra ranged from 87 to 6200 mBq l(-1) which, in some springs, exceed the maximal permissible level of 1 Bq l(-1) for drinking water. Measured activity concentrations of 228Ra ranged from 23 to 3480 mBq l(-1). The study showed that radium content for the investigated thermal and mineral waters is below the levels at which negative consequences would arise due to ingestion.

Radioactive contamination in Croatia by phosphate fertilizer production.

The contents of natural radionuclides (radium, uranium and potassium) were measured in the area of a phosphate fertilizer factory in central Croatia, as a part of extended and still ongoing monitoring program of radioactive contamination of human environment in Croatia that is performed by the Radiation Protection Unit of the Institute for Medical Research and Occupational Health in Zagreb. Activity concentrations in all analysed media (waste water, trickling water from piezometers, phosphogypsum deposit and final products) considerably fluctuated, especially in phosphogypsum and waste water. Mean (226)Ra activity concentration in waste phosphogypsum was measured to be 483+/-190 Bqkg(-1). Based on that value, it was estimated that 4 million m(3) of phosphogypsum that have been deposited up to now contain about 4.3 x 10(12) Bq, i.e. about 200 g of (226)Ra. However, effective dose for an adult that would be incurred by consumption of water from nearby wells was estimated to be 5.3+/-1.3 microSv. The results show that (226)Ra activities cause effective doses, which are below the recommended maximum as the estimated annual (226)Ra effective dose does not exceed 0.1 mSv as recommended by the World Health Organization.

Mosses and some mushroom species as bioindicators of radiocaesium contamination and risk assessment.

Mosses, lichens, mushrooms are able to efficiently accumulate different radioactive elements from their environment to a much higher degree than other vegetation. They are sensitive bioindicators of radioactive contamination for various ecosystems, particularly in the event of a nuclear accident and uncontrolled emission oh fission products. Results of systematic, long-term measurements of 137Cs activities in mosses and in some edible mushroom species in North Croatia for the post-Chernobyl period (1986-2007) are summarized. The study was conducted in the Radiation Protection Unit of the Institute for Medical Research and Occupational Health in Zagreb, as a part of an extensive monitoring program of the Croatian environment. In the overall observed period the highest activity concentration of 137Cs deposited by fallout has been recorded in 1986, which is the year of Chernobyl accident, causing peak S7Cs activity concentration in moss of 8800 Bq/kg in May 1986. In the same period mean 137Cs activity concentration in grass was 390 Bq/kg. The highest value of 137Cs activity concentration in Cortinarius caperatus mushrooms of 1351 Bq/kg has been recorded in 1989. Fitting the measured 137Cs activity concentrations to the theoretical curve the ecological half-life of 137Cs in moss was found to be around 978 days, in grass around 126 days in the period 1986-1990, in Cortinarius caperatus mushroom around 5865 days (16.1 years). Regarding the risk assessment to Croatian population, due to consumption of mushrooms, the collective effective dose for Croatian population, estimated to be about 35 mSv per year, was found to be quite low. Therefore, it can be concluded that mushroom consumption was not a critical pathway for the transfer of radiocaesium from fallout to humans after the Chernobyl accident.

226Ra and 228Ra in Croatian rivers.

The presence of natural radionuclides in Croatian rivers emphasizes the need for its continuous monitoring. Therefore results of 226Ra and 228Ra determination in Croatian river waters are presented in this paper. 226Ra and 228Ra were chosen as a possible source of human exposure due to their high radio-toxicity. Fifty liters of river water samples were collected from the Danube, Drava, Sava, Krka and Neretva rivers twice a year from 2002 to 2006. It is showed that activity concentrations of 226Ra ranged from 6.54 mBq/L to 59.44 mBq/L and 228Ra activity concentrations ranged from 2.57 mBq/L to 20.76 mBq/L. The highest values of both 226Ra and 228Ra were measured in the river Drava, and the lowest values in the river Sava. Statistically significant differences were not observed between radium concentrations from two watersheds (the Black Sea and the Adriatic Sea watershed), nor between 226Ra/228Ra ratio in rivers individually. The number of collected samples is insufficient to make more statistically significant conclusions. However the data obtained in this study could be the baseline for evaluating possible future changes.

Life exposure to 226Ra and possible consequences.

This paper presents a model of continuous exposure to 226Ra by water consumption over a 55-year period. The effects of 226Ra concentration in drinking water were investigated. Reaching the peak at the age of 16, the assessed effective dose has shown that children are more sensitive to radiation than adults. It has been found that consumption of 226Ra-rich water during certain period of life increases consequent effective doses. The earlier the exposure, the higher amount of 226Ra could be retained causing the higher values of effective dose later in life. However, long-term exposure to 226Ra in drinking water as well as consumption of 226Ra-rich water during a certain period of life does not indicate the appearance of malignant diseases in the year of exposure and later in adults.