EDAFOLOGÍA, VOL 15. (1,1 2, 3), PP 155-168 208
EFFECT OF HEXACHLOROCYCLOHEXANE ISOMERS ON SOME SOIL MICROBIOLOGICAL PROPERTIES
Prieto-Fernández A@, Poisa-Beiro L, Acea MJ
Instituto de Investigacións Agrobiolóxicas de Galicia (IIAG-CSIC).
Apartado 122. E-15780 Santiago de Compostela (Spain). Corresponding author:
Ángeles Prieto-Fernández, apf@iiag.csic.es
The effect of heavy contamination with a residue composed of
1,2,3,4,5,6-hexachlorocyclohexane isomers (HCHs) (10, 50 and 100 g HCHs kg-1
soil) on the densities of cultivable soil heterotrophs, algae and N2-fixing
cyanobacteria, on soil microorganisms involved in the N and C cycles (ammonifiers,
amylolytics and cellulolytics) as well as on the ability of soil microbial
communities to degrade several C substrates (community level physiological
profiles, CCLP) was studied. These microbial properties were analysed 2 weeks,
and 2 and 4 months, after the soil was artificially contaminated. The effect
of HCHs residue applied at different concentrations, and in the form of particles
of different sizes on soil respiration was studied. The influence of the presence
or absence of microorganisms from a long term polluted site on the effect of
HCHs on soil respiration was also analysed.
In the short term after the addition of the contaminant to the soil, the density
of heterotrophs increased, the abundance of algae decreased, while the population
of cyanobacteria did not change significantly. Four months after contamination
the effect of the highest concentrations of HCHs (50 and 100 g HCHs kg-1 soil)
on these microbial groups was negative. The HCH residue had a similar effect
on the ammonifying population to that on heterotrophs. The densities of amylolytics
and cellulolytics were either not modified, or were stimulated by the contaminant
in the short term but, in the longer term (4 months after the contamination),
were inhibited by HCHs applied at the highest concentrations. Two months after
contamination, the ability of soil microbial communities to degrade C substrates
(CCLP) was negatively affected by HCHs. It was noteworthy the decrease in the
ability for degrading aminoacids, which was particularly important in the soils
with 50 and 100 g HCHs kg-1 soil.
HCHs also affected soil respiration but the effect depended on the HCH concentration,
particle size of the contaminant, and on the presence or absence of microorganisms
from a long term HCH-contaminated site (adapted to HCH contamination). When
microorganisms adapted to HCH contamination were present and the contaminant
was applied in form of particles of 4-10 mm, the soil respiration was stimulated
by HCH at concentrations between 20 and 100 g HCH kg-1 and inhibited with concentrations
higher than 200 g HCH kg-1 soil. If the HCHs were applied as particles < 1
mm, soil respiration was not stimulated by the contaminant and decreased with
concentrations of 100 g HCH kg-1 or higher. The addition of HCHs in form of
particles of 4-10 mm at concentration of 100 g HCH kg-1 or higher to a soil
with microorganisms non-adapted to the contaminant reduced soil respiration,
while lower concentrations of contaminant did not affect the amount of CO2
evolved.
Key Words: HCH isomers, lindane, soil contamination, soil respiration, soil
microorganisms, soil bacteria