Ž . Advances in Environmental Research 6 2002 523532 Affinity distributions of lead ion binding to an immobilized biomaterial derived from cultured cells of Datura innoxia Shan Lin 1 , Lawrence R. Drake 2 , Gary D. Rayson  Department of Chemistry and Biochemistry, New Mexico State Uni  ersity, Box 30001, MSC 3C, Las Cruces, NM 88003, USA Abstract Datura innoxia biomass has been targeted as a potential sorbent for heavy metal remediation. Of interest in our Ž . laboratory are the binding mechanisms responsible for metal uptake. In this study, the binding behavior of Pb II to immobilized Datura innoxia biomaterial was investigated under different chemical conditions, such as ionic strength, the presence of calcium, and pH. Regularized regression analysis was employed to derive the corresponding affinity distributions. Two classes of binding sites were determined, having mean affinity of approximately 200 and 10 5 M 1 , depending on solution conditions. Variations in apparent affinity distributions with ionic strength and pH suggest the low-affinity sites involve sulfonates and carboxylates in an ion exchange process. The high-affinity sites are proposed to result from the coordination of carboxylates to Pb 2 ions.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Metal ion binding; Binding affinities; Biomaterials; Datura innoxia; Frontal affinity chromatography 1. Introduction Interest in the development of cost-effective meth- ods for the removal and recovery of heavy metals from contaminated waters has greatly increased because of the ecological awareness of the role of metals in the environment. Specifically, recent studies of the detri- Ž mental effects of lead in the environment Buffle et al., . 1990; Davis et al., 1997; Huang et al., 1997 have heightened an interest in the selective removal of this  Corresponding author. 1 Present address: Symyx Technologies Inc., 3100 Central Expressway, Santa Clara, CA 95051, USA. 2 Present address: Los Alamos National Laboratory, CST-9, MS:J514, Los Alamos, NM 87545, USA. Ž toxic heavy metal. Biomaterials, such as algae Fergu- son and Bubela, 1974; Crist et al., 1981; Wood and Wang, 1984; Darnall et al., 1986; Nakajima and Sak- . Ž . aguchi, 1990 , fungi Galun et al., 1984 , organic peat Ž . Ž Stark, 1994 , and Datura innoxia Ke and Rayson, 1992a,b,c,d; Ke et al., 1992a,b, 1994; Drake et al., 1996; . Lin et al., 1996 , have demonstrated the capability to selectively absorb a large amount of various heavy metals. These materials are abundant in nature and potentially inexpensive. Biomaterials have been con- sidered as potential sorbents for heavy-metal remedia- Ž . tion Drake and Rayson, 1996 . However, the inherent Ž complexity of biomaterial systems e.g. chemical het- erogeneity, oligo- or poly-electrolytic or variable charge properties, Buffle et al., 1990; Bartschat et al., 1992; . Nederlof et al., 1993; Schiewer and Volesky, 1995 has made them less predictable than commercial resins 1093-019102$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. Ž . PII: S 1 0 9 3 - 0 1 9 1 01 00078-8