Selected test specimens were also analyzed before and after soil
incubation using scanning electron microscopy (SEM) (Hitachi S-
3500N, Hitachi High Technologies America, Inc., CA, U.S.). Samples
were coated with platinum to a thickness of 0.2 kA using a
Hummer 6.2 sputtering system (Anatech USA, CA, U.S.). A 15 Kv
electron beam was applied.