In laboratory simulations of methane oxidation in landfill cover soil, meth
ane consumption consistently increased to a peak value and then declined to
a lower steady-state value. It was hypothesized that a gradual accumulatio
n of exopolymeric substances (EPS) contributed to decreased methane uptake
by clogging soil pores or limiting gas diffusion. This study was conducted
to detect and quantify EPS in soil from columns sparged with synthetic land
fill gas and from fresh landfill cover cores. Polysaccharide accumulations
were detected with alcian blue stain. EPS was observed adhering to soil par
ticles and as strands associated with, but separate from soil grains. Gluco
se concentrations in laboratory soil columns averaged 426 mg kg(-1) dry soi
l, while in a column sparged with air the average glucose concentration in
a horizon was 3.2 mg glucose kg(-1) dry soil. Average glucose concentration
s in two of four cores sampled from a closed landfill ranged from 600-1100
mg kg(-1) dry soil, while control cores averaged 38 mg glucose kg(-1) dry s
oil. Viscosity due to EPS was measured by comparing filtration rates of soi
l suspensions. Soil extracts from the upper horizons of laboratory columns
sparged with landfill gas filtered at about one-third the rate of extracts
from the lower horizons, and the landfill core with the highest glucose con
tent also produced highly viscous extracts. Breakthrough curves measured in
columns before and after methane exposure were similar, so that shortcircu
iting due to clogging was not occurring. The data support the hypothesis th
at EPS impeded oxygen diffusion to an active biofilm and limited the extent
of methane oxidation. (C) 2000 Elsevier Science Ltd. All rights reserved.