High geogenic arsenic concentrations in travertines and their spring waters: Assessment of the leachability and estimation of ecological and health risks

Highlights

• Curiously high arsenic content found in travertine geobodies in the same vicinity.

• Volcanic substrate main source for high arsenic content.

• pH-dependent leaching tests and single extractions indicate high arsenic mobility.

• Ecological risk assessment of arsenic reflects high potential ecological risk.

• Human health risk assessment reveals adverse non- and high-carcinogenic risks.

Abstract

Travertines and their springs are rarely investigated as a source of toxicity. Remarkably high contents of As (up to 10 g/kg) have been found in travertine deposits and associated spring waters, nearby Ghorveh city (western Iran). Two types of travertines were distinguished: (i) Fissure ridge travertines, in areas with a carbonate-dominated basement, are characterized by a relatively low content and leaching of As. Their spring waters contain > 150 µg/L of As; (ii) Mound travertines, rich in non-carbonate impurities, occur in areas with volcanic substrates and contain high As concentrations (on average ~1,500 mg/kg) with high leachability. Their spring waters have lower As concentrations than equivalent fissure ridge waters. Principal Component Analyses of the elemental and mineralogical composition show the unstable association of As over a wide range of pH values to non-carbonate related elements, in particular iron, related to clay minerals. The high potential release of As may result in adverse ecotoxicological effects in surrounding agricultural soils and crops. An ecological risk assessment confirms the enrichment and very high potential ecological risk of As around mound carbonates. The human health risk assessment based on calculation via exposure factors suggests adverse non-carcinogenic and high carcinogenic risk with regard to As, both for adults and children.

Introduction

Estimating the availability of inorganic pollutants (heavy metals and metalloids) in environmental samples is a crucial step for assessing eco- and human toxicological risks, and for waste management . Increased concentrations of potentially toxic elements (PTEs) can pose severe threats to the environment and human health (Moore et al., 2015a, Moore et al., 2015b, Nematollahi et al., 2020). Arsenic (As), in particular, is a known carcinogen in the lungs, skin, liver, bladder and kidney (IARC, 2004; Fillol, 2010). Several studies also point out the potential toxicological impact of As (e.g. States et al., 2009, Argos et al., 2012, Kundu et al., 2011). Long-term exposure to As may lead to vascular and skin diseases (Wang et al., 2003, Wang et al., 2007, Kapaj et al., 2006, Khan et al., 2009). In addition, some authors (Antoniadis et al. 2019) suggest that the risk of As exposure tends to be often underestimated Despite that anthropogenic activities can concentrate PTEs in soil, water, sediments and rocks, elevated concentrations could also be geogenic in origin. According to Dradrach et al. (2020), As release from As-rich rocks can enter a more active biogeochemical cycle and subsequently pose a substantial risk to ecosystems, usually due to rock weathering (Myrvang et al. 2016). A vast amount of publications address As contamination by anthropogenic sources (e.g., Rinklebe et al., 2019, Mensah et al., 2020), however, only a few studies focused on geogenic rock-sourced As (e.g., Horckmans et al., 2005, Di Benedetto et al., 2006, Costagliola et al., 2013, Winkel et al., 2013). Often, directly or indirectly, elevated concentrations can be linked to the geology of a specific location. Therefore, local background concentrations of PTEs in soils and sediments should be used as a reference value to estimate the potential anthropogenic contamination and/or geogenic enrichment level of soils and sediments (De Saedeleer et al., 2010, Moore et al., 2015a, Moore et al., 2015b). Even when measured concentrations significantly exceed common background values, As anomalies do not necessarily pose health issues. An important determinant is its mobility in rocks, sediments, soils and water. Only soluble As, for example, can be taken up by plants (Bissen and Frimmel, 2003). pH is one of the key parameters controlling directly or indirectly the mobilization or retention of heavy metals and As in sediment, soils and waste materials (Van Herreweghe et al., 2002), and thus will largely influence heavy metal and As behavior and their toxicity. Sediments and soils with different mineralogical, physical and chemical properties but similar total concentrations of As may, therefore, display different risks to the environment and human health (CCME, 1995). Regardless of the geogenic or anthropogenic origin of PTEs, each situation should always be critically evaluated for potential ecological and health risks.

In this study, two travertine deposits that occur contiguously, but display different morphology and textural framework, as well as geochemical signatures, were selected for a thorough petrographical (Mohammadi et al., 2019) and geochemical study. The first travertine type dominantly possesses a sparitic fabric consisting of almost pure calcite and a low content of non-carbonate components; while the second travertine body displays a dominant micritic fabric consisting of fine-crystalline calcite with a relatively high non-carbonate content, mainly consisting of clay minerals. Chemical analyses of the latter revealed high As concentrations. The question that then naturally arises is whether the active alkaline springs and rivers, that pass through these travertine bodies and which irrigate the agricultural land of rice and wheat, also contain high As concentrations. Therefore, the three main aims of this study are (1) determining the concentration of As and associated elements in travertines with different fabric and in their spring waters; (2) assessing the leachability/mobility of As in the travertines; and (3) carrying out a simplified ecological and health risk assessment.