Absorption of selenium by Lactuca sativa as affected by carboxymethylcellulose B. Pezzarossa a, * , G. Petruzzelli a , F. Petacco a , F. Malorgio b , T. Ferri c a CNR, Istituto per lo Studio degli Ecosistemi, sede di Pisa, Via Moruzzi 1, 56124 Pisa, Italy b Dipartimento di Biologia delle Piante Agrarie, Universita ` di Pisa, Italy c Dipartimento di Chimica, Universita ` ‘‘La Sapienza’’, Roma, Italy Received 24 February 2006; received in revised form 26 September 2006; accepted 27 September 2006 Available online 14 November 2006 Abstract Several organic compounds of high molecular weight present in soil interact with selenium and may act as active binding agents affect- ing its availability in soil, and, consequently, selenium uptake by plants. This study is aimed at investigating the effects of polysaccharides on selenium speciation in soil and on selenium absorption by Lactuca sativa L. plants. Three-week-old seedlings were transplanted into pots filled with soil, and sodium selenite at rates of 1.5 and 5 mg Se kg À1 of soil, or sodium selenate at a rate of 1.5 mg Se kg À1 of soil were applied. Carboxymethylcellulose (CMC) was added to the soil at rates of 0, 3 and 30 mg kg À1 of soil. After 48 and 110 d from trans- planting plants were harvested, separated into root and shoot, and fresh and dry matter weights were recorded. Total selenium was deter- mined in both soil and plant samples. A sequential extraction was used to investigate the different Se oxidation states and assess the availability of Se in soil after the final harvesting. Both selenite and selenate were absorbed by roots, but plants amended with Se VI+ showed higher selenium concentration than plants amended with Se IV+ . Selenite appears to be less mobile than selenate both in soil and plants. The addition of carboxymethylcellulose to soil decreased the amount of selenium absorbed by plants. CMC interacted with Se, making it less mobile as evidenced by the increase in the insoluble fractions. The insoluble Se forms in soil may represent environ- mental Se sinks potentially available for plants if the substrate is re-used for subsequent growth cycles and selenium species are mobilized as a result of biological and chemical processes. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Selenite; Selenate; Vegetable crops; Polysaccharide; Speciation 1. Introduction Selenium (Se) has been recognized to be an essential nutrient for animals, humans and microorganisms, but to be toxic at levels little above those required for health and the range between its essentiality and its toxicity is quite narrow (Wilber, 1980). Se in the diet is obtained from animal and plant prod- ucts, including cereals, grains and vegetables. Selenium is absorbed by plants from soil and converted mainly into Se–methionine which is incorporated into proteins in place of methionine and can account for more than 50% of the total Se content in plant. Se plays a prominent role in glu- tathione peroxidase (GSH–Px) selenoproteins for the cellu- lar antioxidant defence system and thus in the prevention of DNA damage, cancer initiation, and cancer progression (Tapiero et al., 2003). The anticarcinogenic activities of some Se forms against colon, lung, skin and other types of cancer have been demonstrated (Eder et al., 2003; Strat- ton et al., 2003; Swede et al., 2003). Selenium deficiency has been a widespread problem in domestic and wild species of grazing ruminants and in humans in China, Nepal, Australia, and Central Africa. Diseases, such as the ‘white muscle disease’, a myopathy affecting both cardiac and skeletal muscles, are usually asso- ciated with lowered reproductivity and growth efficiency of 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.09.073 * Corresponding author. Tel.: +39 050 3152488; fax: +39 050 3152473. E-mail address: beatrice.pezzarossa@ise.cnr.it (B. Pezzarossa). www.elsevier.com/locate/chemosphere Chemosphere 67 (2007) 322–329