title: Metal and anion composition of two biopolymeric chemical stabilizers and toxicity risk implication for the environment.
abstract: The objective of this study was to (1) measure the concentration of four anions (Cl(-), F(-), [image omitted], and [image omitted]) and nine other elements (Al, Ba, Ca, K, Mg, Mn, Fe, Ni, and Si) in two nontraditional biopolymeric chemical stabilizers (EBCS1 and EBCS2), (2) investigate consequent environmental toxicity risk implications, and (3) create awareness regarding environmental health issues associated with metal concentration levels in enzyme-based chemical stabilizers that are now gaining widespread application in road construction and other concrete materials. Potential ecotoxicity impacts were studied on aqueous extracts of EBCS1 and EBCS2 using two thermodynamic properties models: the Pitzer-Mayorga model (calculation of the electrolyte activity coefficients) and the Millero-Pitzer model (calculation of the ionic activity coefficients). Results showed not only high concentrations of a variety of metal ions and inorganic anions, but also a significant variation between two chemical stabilizing mixtures. The mixture (EBCS2) with the lower pH value was richer in all the cationic and anionic species than (EBCS1). Sulfate (SO(2-)(4)) concentrations were found to be higher in EBCS2 than in EBCS1. There was no correlation between electrolyte activity and presence of the ionic species, which may be linked to a possible high ionic environmental activity. The concentrations of trace metals found (Mn, Fe, and Ni) were low compared to those of earth metals (Ba, Ca, K, and Mg). The metal concentrations were higher in EBCS1 than in EBCS2. Data suggest that specific studies are needed to establish "zero" permissible metal ecotoxicity values for elements and anions in any such strong polyelectrolytic enzyme-based chemical stabilizers.
authors.affiliation: Department of Chemistry, Tshwane University of Technology, Arcadia 0001, Pretoria, Republic of South Africa. ndibewup@ tut.ac.za
authors.forename: P P
authors.initials: PP
authors.lastname: Ndibewu
authors.forename: M B
authors.initials: MB
authors.lastname: Mgangira
authors.forename: N
authors.initials: N
authors.lastname: Cingo
authors.forename: R I
authors.initials: RI
authors.lastname: McCrindle
mesh_terms: D000838:Anions / Q000737:chemistry* / Q000633:toxicity*; D001704:Biopolymers / Q000737:chemistry* / Q000633:toxicity*; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000737:chemistry / Q000633:toxicity; D008670:Metals / Q000737:chemistry* / Q000633:toxicity*; D012307:Risk Factors
chemical_list: D000838:Anions; D001704:Biopolymers; D004785:Environmental Pollutants; D008670:Metals