Removal of Cr, Ni and Co in the water of chromium mining areas by using Lemna gibba L. and Lemna minor L Ahmet Sasmaz 1 , Ibrahim Mete Dogan 2 & Merve Sasmaz 3 1 Department of Geological Engineering, Firat University, Elazı g 23119, Turkey; 2 Etikrom A.S¸.PK. 96, Elazig, Turkey; and 3 Department of Environmental Engineering, Firat University, Elazı g 23119, Turkey Keywords accumulation; heavy metals; Lemna gibba L.; Lemna minor L.; mining water; water treatment. Correspondence A. Sasmaz, Department of Geological Engineering, Firat University, Elazı g 23119, Turkey. Email: asasmaz@gmail.com doi:10.1111/wej.12185 Abstract This study investigated the use of Lemna gibba and Lemna minor plant species to absorb Cr, Ni and Co from Alacakaya mining area water. Lemna gibba and L. minor were separately placed to feed into two reactors. Water and plant samples were collected for eight consecutive days, and the pH, electric conductivity and temper- ature of the water were measured. The plants were washed, dried and burned at 3008C for 24 h in a drying oven. The samples were then analysed by ICP-MS (induc- tively coupled plasma mass spectroscopy) for concentrations of Cr, Ni and Co, which were 1.2, 0.9 and 0.5 lgL 21 respectively. On Day 8, the determined uptake of L. gibba and L. minor were: 196 and 398% for Cr; 307 and 1473% for Ni; and 166 and 223% for Co respectively. Lemna gibba and L. minor were thus effective in absorbing Cr, Ni and Co from mining water. Introduction Heavy metals (HM) have a high atomic weight and a density at least five times greater than that of water (Tchounwou et al. 2012). HM pollution in aquatic environments is one of the main problems affecting plant and animal lifes (Duffus 2002). HMs are classified into two categories by Gergen & Harmanescu (2012) and Rai et al. (2015) that these metals have no beneficial role and are positively toxic to lives, such as Ni, Cd, Hg, Pb, Cr and As. In contrast, metals such as Co, Fe, Cu, Cr (13), Mn, Zn are essential for plant and animal life but may become toxic if the concentrations are too high. HM toxicities depend on several factors, including chemical spe- cies, route of exposure, dose, nutritional status, gender and genetics. Arsenic, mercury, chromium, lead and cadmium are prioritised in term of public health significance because of their high degree of toxicity (Tchounwou et al. 2012). Due to industrial and mining activities, toxic heavy metals such as As, Pb, Hg, Cd, Cr, Ni, Fe, Cu, Co and Zn have caused wide- spread water, air and soil contamination (Rai et al. 2015). Chromium (Cr) enters into natural ecosystems from indus- trial activities such as iron and steel manufacturing, chro- mium plating, wood preservation, chrome leathering, smelting processes, mining, fuel production, industrial out- flow and other anthropogenic sources (OECD 2003). Cr toxic- ity in plants is connected with its valence state: Cr (III) is less toxic, whereas Cr (VI) is highly toxic and also mobile (Shanker et al. 2005). There is no evidence to suggest that Cr and Ni play an essential role in plant metabolism, although high concentrations of Cr and Ni are known to have toxic effects on both plants and animals (Sun e et al. 2007; Kabata-Pendias 2011; Drzewiecka et al. 2012). However, the antioxidative enzymatic system of plants can be stimulated under Ni stress, helping them to tolerate high Ni concentrations (J ocs ak et al. 2008; Gonzalez et al. 2015). Cobalt (Co) is essential for blue-green algae and microorganisms, although there is some evidence that it has a beneficial effect on plant growth, whether it is in fact essential for plant life remains unclear. Co is a component of vitamin B 12 , which is its only known function (Pais & Jones 2000). According to Environ- ment Canada’s 2013 report, 2.5 lg Co 21 L 21 is considered as nontoxic. Of the different techniques for removing of heavy metals, phytoremediation is among the cost-effective and ecologi- cally friendly, in that it uses living green plants for in situ removal of contaminants from water and soil (Sood et al. 2012; Tatar & Obek 2014; Goswami et al. 2014; Sasmaz et al. 2015). Phytoremediation depends on the ion uptake mecha- nism, as well as the physiological, anatomical and morpho- logical characteristics of each species (Rahman & Hasegawa 2011). Floating macrophytes usually uptake metal or con- taminants through the process of rhizofiltration (Chaudhuri et al. 2014). Lemna sp. has been selected because of its faster growth rate and easer harvest, in phytoremediation 1 Water and Environment Journal (2016) V C 2016 CIWEM. Water and Environment Journal. Print ISSN 1747-6585