Size-dependent toxicity of ThO2 nanoparticles to green algae Chlorella pyrenoidosa.

Thorium (Th) is a natural radioactive element present in the environment and has the potential to be used as a clean nuclear fuel. Relatively little is known about the aquatic toxicity of Th, especially in nanoparticulate form, which may be the main chemical species of Th in the natural waters. In this study, impacts of ThO2 nanoparticles (NPs) with two different sizes (52 ± 5 nm, s-ThO2vs. 141 ± 6 nm, b-ThO2) on a green alga Chlorella pyrenoidosa (C. pyrenoidosa) were evaluated. Results indicated that C. pyrenoidosa was more sensitive to s-ThO2 (96-h EC30 = 64.1 µM) than b-ThO2 (96-h EC30 = 100.2 µM). Exposure to 200 µM of ThO2 NPs reduced the chlorophyll-a and chlorophyll-b contents of the algal cells. At 96 h, SEM and TEM showed that more agglomerates of s-ThO2 than those of b-ThO2 were attached onto the surface of algal cells. Reactive oxygen species (ROS) generation and membrane damage were induced after the attachment of high concentrations of ThO2 NPs. The heteroagglomeration between ThO2 NPs and algal cells and increased oxidative stress might play important roles in the toxicity of ThO2 NPs. To the best of our knowledge, this is the first report on aquatic toxicity of ThO2 NPs.

The German Thorotrast Cohort Study: a review and how to get access to the data.

It is well known that exposures like those from (226)Ra, (224)Ra and Thorotrast(®) injections increase the risk of neoplasia in bone marrow and liver. The thorium-based radioactive contrast agent Thorotrast(®) was introduced in 1929 and applied worldwide until the 1950s, especially in angiography and arteriography. Due to the extremely long half-life of several hundred years and the life-long retention of the thorium dioxide particles in the human body, patients suffer lifetime internal exposure. The health effects from the incorporated thorium were investigated in a few cohort studies with a German study being the largest among them. This retrospective cohort study was set up in 1968 with a follow-up until 2004. The study comprises 2326 Thorotrast patients and 1890 patients of a matched control group. For those being alive at the start of the study in 1968 follow-up was done by clinical examinations on a biannual basis. For the others, causes of death were collected in various ways. Additionally, clinical, radiological and biophysical studies of patients were conducted and large efforts were made to best estimate the radiation doses associated with incorporation of the Thorotrast. The aim of this paper is to describe the cohort, important results and some open questions. The data from the German Thorotrast Study are available to other interested researchers. Information can be found at http://storedb.org .

The uneven irradiation of a target cell and its dynamic movement can mathematically explain incubation period for the induction of cancer by internally deposited radionuclides.

Irradiation from internally deposited radionuclides induces malignant tumors. Ingested radionuclides accumulate in specific organs, which are irradiated over a lifelong period. Our aim is to elucidate why the development of malignant tumors requires long-term internal exposure, on the order of decades, despite the fact that irradiation is continuous over this period. Three major factors are considered to be responsible for the long incubation time in carcinogenesis caused by internally deposited alpha-emitters: uneven distribution of radionuclides, limited range of irradiation, and dynamic movement of tumor precursor cells. We hypothesized that target cells susceptible to malignant transformation may undergo one event by alpha particles and may then migrate outside of the range of alpha particles, thereby avoiding immediate induction of successive additional events that would lead to cell death or neoplastic changes. Based on this hypothesis, we further proposed a mathematical model to predict the relationship between dose rate and incubation period of tumors induced by internally deposited alpha-emitters. The function was non-linear and included terms of both direct and indirect radiation effects. It well fitted both human Th-ICC cases and rat Pu-induced lung cancer, suggesting that indirect radiation effects are independent from dose rate. The significance of parameters of the model is discussed.

Ras gene mutations in vinyl chloride-induced liver tumours are carcinogen-specific but vary with cell type and species.

Previous studies have shown that a high proportion (5/6) of human liver angiosarcomas (ASL) associated with exposure to vinyl chloride (VC) contains a GC-->AT mutation at the Ki-ras codon 13. This mutation, however, has not been found in 5 ASL or 2 hepatocellular carcinomas (HCC) induced in rats by VC. These 2 HCC did contain a mutation at codon 61 of the Ha-ras gene. In order to extend this study and further explore the mechanisms of tumour induction, an additional 6 ASL and 6 HCC induced in rats by VC were analysed for ras gene point mutations, as well as 10 rat and 10 murine ASL induced by vinyl fluoride (VF), and 5 ASL, 6 Kupffer cell sarcomas, 4 HCC and 2 cholangiocellular carcinomas induced by Thorotrast in rats. Tumour DNA was analysed by PCR-SSCP and direct sequencing. None of the rodent ASL contained a mutation at codon 13 of the Ki-ras gene showing that the ras gene mutational pattern is species-specific. The CAA-->CTA mutation, previously found at codon 61 of the Ha-ras gene in rat HCC, was observed in 5 further VC-induced HCC but was not detected in the Thorotrast-induced HCC, suggesting carcinogen-specificity. This mutation was also absent in VC-induced ASL, which supports the cell-specificity of the ras mutational pattern in chemically induced tumours. No predominant mutation was detected in VF- and Thorotrast-induced tumours. Thus, a given mutation in a tumour may be carcinogen-specific but also depend on the species and the cell type.

The effects of Thorotrast and quartz on the induction of lung tumors in rats.

In a long-term animal study, the combined and separate effects of Thorotrast (colloidal 232ThO2) and silica dust on the induction of lung tumors were investigated. Female Wistar rats were exposed for 29 d to aerosol concentrations of quartz of either 6 mg m-3, 30 mg m-3, or 0 mg m-3 (6 h d-1, 5 d wk-1). After inhalation, one-half of all exposed animals received a single intravenous injection of enriched Thorotrast (600 microL, 2960 Bq 228 Th mL-1). In all quartz-exposed groups the incidence of benign and malignant lung tumors turned out to be more than 40%. The additional Thorotrast treatment (lifelong exhalation of 220Rn) led to a marked shortening of latency times (first lung tumor was found 1 y after treatment) and to a higher total incidence in the animals exposed to 30 mg m-3 quartz (57 of 87 animals with lung tumors = 65.5%). In the group treated only with Thorotrast, three of 87 animals developed lung tumors. Statistical methods that correct for intercurrent mortality showed a significant increase of the lung tumor risk with respect to Thorotrast treatment, even for the low quartz groups with nearly similar incidences of lung tumors (in the group with ThO2, 39 out of 87 = 44.8%; in the group without ThO2, 37 out of 82 = 45.1%). The tumors were found predominantly in the peripheral regions of the lung and were preceded by proliferation and hyperplasia of the alveolar and bronchiolar epithelium. The results demonstrate a pronounced interactive effect of quartz and Thorotrast on carcinogenesis of the lung. The underlying possible mechanisms are discussed.

Recent results of the German Thorotrast study--dose relevant physical and biological properties of Thorotrast equivalent colloids.

As a prerequisite for quantifying the non-radiation effect of Thorotrast, nonradioactive and radioactive aquasols with identical physicochemical properties and with biophysical behavior comparable to that of Thorotrast were developed and produced for a second long-term animal experiment. Comparative investigations with hafnium and zirconium (zirconotrast) dioxide aquasols showed the latter to be most appropriate considering the size of both the dispersoids and the aggregates in the liver tissue. The average particle diameters of ThO2, ZrO2 and HfO2 proved to be values of 9.3 nm, 15 nm and 45 nm, respectively. The size of the aggregates shows a slight dependence on the applied amount but no dependence on the duration of body burden of the colloid. The aggregate diameters in the 600 microliters group turned out to be 9.6 microns, 14.4 microns and 5.3 microns, respectively. Radioactive zirconotrast was prepared by radiochemical incorporation of 230Th and 228Th at dose rates which produce accumulated doses in the liver of rats equivalent to those of commercial 230Th enriched Thorotrast after 1.5 yr. Five different colloids were prepared with alpha-energy emission rates increased by factors of 1, 2.5, 5, 10 and 25 compared to Thorotrast and then injected into rats.