Proposed relationships between the surfactant properties and the developmental toxicity induced in frog embryos of Humic acid.
Humic acid (HA) is as an anionic surfactant that promotes the
mobilization of a non-aqueous phase liquid (NAPL) in a porous medium. HA
is extracted from peat by a simple series of acid/base extractions. The
critical micelle concentration (CMC) was determined as the lowest
concentration of HA needed to produce maximal effect on the surface
tension in distilled water. Short-column tests of a HA solution at the
critical micelle concentration (CMC) of 3.4 mg/ml were used to evaluate
the applicability of HA as a surfactant. HA improved the NAPL removal
efficiency up to about 81% as measured by simple column flushing tests.
HA developmental toxicity was also tested using the Frog Embryo
Teratogenesis Assay-Xenopus (FETAX) methods. ToxTools[R] was used to
estimate 50% effect levels, 30% and 10% effect levels for HA. The 96-hr
LC50 was approximately 4.0 mg/ml and the 96-hr EC50 (malformation) was
greater than 4.05 mg/ml and therefore could not be estimated accurately.
Although malformations were observed, no significant teratogenic effect
is evident for HA in Xenopus embryos. The HA has an LC50 in the vicinity
of the CMC, which is the optimum concentration for using the HA as a
surfactant. This indicates that the toxicity maybe due to the disruption
of cell membranes. This work was supported in part by a Faculty Research
Grant from JSU.
James R. Rayburn, David Steffy, And Cody St. John. Biology
Department, Jacksonville State University, Jacksonville, AL. 36265