Understanding the extent of human health risks with an emphasis on carcinogenesis development attributable to potentially toxic chemicals is critical to effective prevention and mitigation strategies. Chromium (Cr), mainly the hexavalent chromium (Cr (VI)), is a chemical associated with cancer when found in drinking water, making it a major public health issue. This study assessed a possible carcinogenic human health risk among the general population due to exposure to total or hexavalent chromium. We performed a systematic review of the international scientific literature, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol to determine the human risk of cancer mortality and morbidity. In total, 76 articles were checked for eligibility, 13 of which were included in the final systematic review. Only scientific articles from January 2000 to November 2022 published on PubMed were included. Data from both epidemiological ecological studies (Relative Risk and Rate Ratio—RR and Standardized Mortality Rate—SMR) and epidemiological case studies (Lifetime Cancer Risk—LCR, Incremental Lifetime Cancer Risk—ILCR, Cancer Risk—CR, Hazard Quotient—HQ, Hazard Index—HI, Health Risk Assessment—HRA, Disability-Adjusted Life Year—DALY, and Chronic Daily Intake Index—CDI) were included for the overall assessment of carcinogenicity in the general population. According to most articles, there is credible evidence that hexavalent chromium via water is indicated as a major contributor to the global burden of cancer in humans. Some of them emphasize malignant neoplasms in the lung, liver, stomach, and genitourinary system. Although the health index data of the case studies are based on a limited number of samples, they raise concerns about the possibility of an increase in the degree of carcinogenesis. However, there are significant limitations due to the lack of information on the dose and duration of exposure in the target group. Further research involving extensive analysis of the association of the two variables is needed, which depends on more complete information extraction and advanced methodologies.

Hexavalent chromium (Cr (VI)) is an environmental contaminant brining high concerns due to its higher toxicity and mobility in comparison with trivalent chromium Cr(III). Cr (VI) has been linked with several adverse health effects, including respiratory diseases, lung cancer, and skin irritation. The primary sources of it in the environment are industrial activities.Most of the time, fly ash made of lignite can release Cr(VI) when it comes into contact with water in an aquatic environment. The objective of this study is the investigation of Cr (VI) concentration in leachates of fly ash and marl mixtures and the determination of its solubility under different pH conditions. Samples of fly ash were collected from the Power Plant of Agios Dimitrios. Additionally, samples of marl were collected from the mine of South Field, and both samples were mixed and prepared in in different proportions (% w.t.). The leaching experiments were carried out according to the EN-12457/1-4 (2003) standard under different pH conditions and chemical analysis of the leachates were performed by spectrophotometry with diphenylcarbazide (DPC). The environmental footprint of Cr (VI) in the study area was significant, especially in mixtures containing higher concentrations of fly ash. A critical pH range between 6 to 12 is observed. At acidic pH values, a high release of Cr (VI) was observed, while at the mentioned critical values (pH 10–12), a gradual decrease in its leachability was noticed. The high concentrations of Cr (VI) in the industrial area studied require immediate actions in terms of managing and limiting the potential hazardous impacts on the environment and by extension on the public health by developing appropriate prevention strategies. Graphical abstract

Fifteen (15) zeolitic rocks from Karlovassi-Marathokampos basin of Samos Island (Greece) were investigated for their mineralogical composition by X-Ray Diffraction (XRD) method. According to EU Regulation No 651/2013, clinoptilolite of sedimentary origin with ≥80 wt% clinoptilolite, ≤20 wt% clay minerals, free of fibres and quartz, can be used as feed additive for all animal species. Depending on the zeolites, the zeolitic rocks are grouped to those containing: Clinoptilolite (33-86 wt%), clinoptilolite (59 wt%) + mordenite (20-21 wt%), clinoptilolite (22 wt%) + analcime (29 wt%), clinoptilolite (17 wt%) + phillipsite (27 wt%), analcime (29-70 wt%), mordenite (62%) and chabazite (63 wt%). None of the clinoptilolite-containing rocks (10 samples) meet the requirements of the EU Regulation No 651/2013, and thus cannot be used as feed additives for all animal species and consequently as nutrition supplements, since all of them contain 2-5 wt% quartz, two of them 20-21 wt% mordenite (fibrous zeolite), nine of them 20 wt% clay minerals (27-42 wt%). Although the EU Regulation No 651/2013 refers to clinoptilolite of sedimentary origin, using the presence or absence of quartz and fibrous minerals, none of the five mordenite, analcime and chabazite containing zeolitic rocks, can be used as feed additives and nutrition supplements, since all of them contain 2-6 wt% quartz and one of them contains 62 wt% mordenite (fibrous zeolite).

High quality natural zeolites may have insecticidal effects and could be used for pest control. We determined the mineralogical and chemical composition of four representative samples of zeolite-rich rocks (zeot1–zeot4) collected from north-eastern Greece and their oviposition deterrent effect for the olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae). Samples zeot1–zeot4 contain 54–70 wt.% clinoptilolite (HEU-type zeolite) and are free of fibrous minerals. Regarding the chemical composition, samples zeot1–zeot4 contain SiO₂ between 64.29 (zeot4) and 68.03 wt.% (zeot3). The values of the sorption ability ranged from 134 to 195 meq/100 g, and the specific surface area ranged from 6.5 to 8.4 cm²/g. In addition, the concentration of toxic heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Se, V, and Zn) is very low and within the acceptable limits for the food sector. When females of the olive fruit fly had access to olive fruits treated with aqueous suspensions of zeot1–zeot4, a significant oviposition deterrent effect was observed. The highest oviposition deterrent effect was observed after the application of zeot3 on the olive fruits, i.e., the mean number of eggs laid by 5 females on the treated and non-treated (control) olive fruits after 8 days was 43.1 and 172.3, respectively. Among the tested zeolites, zeot3 had the highest levels of HEU-type zeolite (clinoptilolite), SiO₂, Si, and Ca and the strongest sorption ability and specific surface area. The zeolites oviposition deterrent effect found in our experiments can be attributed to the creation of a thin layer (hymen) of natural zeolite on the surface of the olive fruits which inhibits females landing and egg laying. The oviposition deterrent effect of high-quality Greek zeolites with unique characteristics, if verified with field experiments, could improve the effective control of the olive fruit fly.

The zeolitic rocks of Akrotiri, on Santorini Island (Aegean Sea, Greece), can be grouped according to the zeolite minerals present. The first group includes zeolitic rocks that contain only clinoptilolite, the second group contains clinoptilolite and mordenite and the third group contains only mordenite. Clinoptilolite accounts for up to 56 wt.% and mordenite for up to 69 wt.% of the rocks. All samples contain feldspars (8–36 wt.%), clay minerals (6–8 wt.%), quartz (3–6 wt.%), opal-CT (2 wt.%), amphibole (2–4 wt.%) and amorphous materials (4–7 wt.%). The studied samples were classified chemically as andesites or dacites. The ammonium-exchange capacity of the studied samples was 104–158 meq 100 g^–1. According to Commission Implementing Regulation (EU) No. 651/2013, zeolitic rocks that contain ≥80 wt.% clinoptilolite, ≤20 wt.% clay minerals and are free of fibrous minerals and quartz can be used as feed additives in animal husbandry. Zeolites with fibrous habit (mordenite, erionite, secondarily roggianite and mazzite) and SiO₂ minerals such as quartz, cristobalite and tridymite can be dangerous to both humans and animals. The mineralogical study showed that, due to their low clinoptilolite content and the presence of both quartz and fibrous mordenite, the studied zeolitic rocks do not conform with European Regulation No. 651/2013. As a result, their use as feed additives and nutrition supplements is prohibited.

Significant environmental issues concerning the risk of soil, surface, and groundwater pollution are indicated by the presence of dissolved elements in the leachates. In the Lignite Center of Western Macedonia, the current study investigates the leaching behavior of main and trace elements from fly ash-marl mixtures, focusing on the effect of pH conditions on environmental impacts. Five mixtures of fly ash-marl were prepared in different percentage ratios by weight, simulating the possible deposition conditions to investigate the leaching of their contents in specified pH conditions. Initial fly ash is enriched in CaO, SO3, P2O5, and MgO, exceeding continental crust average composition in U, Br, Sb, Ni, Cd, W, and Mo. In contrast, the original marl is enriched in CaO and Ni but depleted in other major elements. The pH significantly affects leaching, with high concentrations of Ca2+ both in fly ash and in mixtures with high concentrations of fly ash, particularly at pH 8. Significant leaching of Cr and Ni is observed, with Cr mainly from fly ash at pH 10–12 and Ni increasing in marl at pH 6. The findings highlight the significant role of fly ash in the environmental element release and the importance of effective management.