2.4. Microbial Biomass N (MBN)
Soils were exposed to the dispersant at same ratios as used in
the Hamdan and Fulmer (2011) study, at Corexit:wet soil ratios
of 0:10, 1:10, 1:100, 1:1000 and 1:10000 for 5 d under anaerobic
condition, after which MBN was measured. These rates also provided
a broad range in order to determine critical toxic thresholds
to the microbial consortia. Microbial biomass N was determined
using the chloroform fumigation extraction method (Brookes
et al., 1985) with modifications by White and Reddy (2000) by
extracting a set of controls with 25 mL of 0.5 M K2SO4 at a ratio
of approximately 1:50 (g dry soil:extractant). A duplicate set of
samples underwent chloroform fumigation in a vacuum-sealed
glass desiccator containing a 100 mL beaker with chloroform over
a 24 h period. Samples were centrifuged for 10 min at 4000g, vacuum-
filtered through Whatman #42 filter and analyzed using a
Shimadzu TOC-V CSN Analyzer (White and Reddy, 2003).