Journal of Hazardous Materials 166 (2009) 1332–1338 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation Pattiyage I.A. Gomes, Takashi Asaeda ∗ Department of Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8770, Japan article info Article history: Received 29 August 2008 Received in revised form 4 November 2008 Accepted 10 December 2008 Available online 14 December 2008 Keywords: Calcium Chromium Nitella pseudoflabellata Phycoremediation abstract This article discusses the applicability of the Charophyte, Nitella pseudoflabellata in the remediation of Cr (VI) contaminated waters at different calcifying potentials. Its growth was found to be positively correlated with Ca in water (CaW), but marginally significant in the presence of Cr (VI) in water (CrW). High CaW resulted in calcite encrustation on the plant cell wall. CaW was found to be aiding Cr (VI) fixation in the long run, as this correlated positively with both CaW and CrW. However, Ca interfered with passive Cr (VI) accumulation in live plant matter at low CrW concentrations (≤0.2 mg/L). Biosorption by dead plant matter seemed to be the major mechanism as the dead plant organs contained >1 mg/g Cr dry weight of plant. Cr (VI) concentrations greater than 0.4 mg/L were too toxic, showing maximum quantum efficiency of PSII photochemistry (F v /F m ) values < 0.63. The opposite was noticed (F v /F m > 0.76) when Cr (VI) was less than 0.2 mg/L. Elongation curve patterns based on shoot lengths showed similar scenarios. In all cases high CaW units with calcite encrustation found to be least affected by Cr (VI) toxicity. Optimum remediation was obtained using a combination of high Ca and Cr (VI) in the case of passive (short-term) operation and low Ca and Cr (VI) for active (long-term) operation. Under the passive scenario, plants accumulated above 1.2 mg/g Cr dry weight whereas in the active case, accumulation was 0.8 mg/g Cr dry weight. We conclude that Nitella-mediated Cr (VI) remediation is a promising technique within the range and conditions investigated. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Charophytes, the growth form of characean algae, are an obvi- ous form of aquatic vegetation in many quiescent water bodies. Characeae occurs in a wide range of water bodies: fresh to brackish and temporary to permanent [1]. It is often argued that the exis- tence of Charophytes indicates healthy, clear water ecosystems. However, some authors have reported it to be a nuisance plant [2]. Many forms of Charophytes are subject to calcification [3], which in the form of CaCO 3 takes place on stems, branchlets and on the sur- face of oogonia [4]. Calcification accompanies the photosynthetic utilization of bicarbonate [5,6]. Bicarbonate assimilation requires an equal input of photons, thus plants rely on diffusion to sup- ply photon equivalents. This will make them to bath in an alkaline, CO 2 depleted micro-environment [5]. Therefore, as a means of over- coming this problem, Charophytes cycle protons through their cells, creating acidic and alkaline zones [5]. CaCO 3 deposition will be on these alkaline regions. McConnaughey [5] and Vymazal [7] showed that heavily calcified plants exhibit high rates of photosynthesis due ∗ Corresponding author. Tel.: +81 80 3173 5312; fax: +81 48 858 9574. E-mail address: asaeda@mail.saitama-u.ac.jp (T. Asaeda). to a lower amount of leakage of CO 2 from cells to alkaline zones, as CaCO 3 reduces the permeability of the alkaline surface. Most aquatic plants under hard water conditions are capable of precipitating calcite (CaCO 3 ) [8,9]. However, in most cases, the CaCO 3 is dispersed and not associated with the plants themselves [7,9]. Furthermore, Charophytes have a higher calcifying potential than other aquatic plants [9]. Van den Berg et al. [10] reported that Charophytes contain CaCO 3 at levels as high as 60% per dry weight. It is also reported that many heavily calcified Charophytes get deposited in aquatic environments leading to the formation of maerl [3,7]. Among Charophytes, Chara and Tolypella spp. are more frequently calcified than those of Nitella spp. [4]. Due to various anthropogenic activities, heavy metals are released into water bodies. Their mobility and bioavailability could drastically disturb the ecological balance [11,12]. However, phy- toremediation (the use of plants and their associated microbes for environmental cleanup) has gained acceptance as a cost effective, non-invasive alternative to the presently available physicochem- ical pollutant remediation techniques [11]. Remediation by algae (phycoremediation) too is considered as a viable option of heavy metal remediation [13]. Hyperaccumulation of metals by Charo- phytes were first reported in 1975 for manganese accumulation [14,15]. However, literature pertaining to the remediation of toxic heavy metals by Charophytes is scarce to our knowledge. 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.12.055