Research Short-Term Changes in Bacterial Community Fingerprints and Potential Activities in an Alfisol Supplemented with Solid Waste Leachates FRANCK POLY,† RAPHAEL GROS,‡ L U C I L E J O C T E U R - M O N R O Z I E R , * ,† A N D YVES PERRODIN§ UMR CNRS 5557 Ecologie Microbienne, Bat. Gregor Mendel, 16 rue Dubois, Universite´ Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France, Laboratoire Science du sol CISM-Universite´ de Savoie, 73376 Le Bourget du Lac Cedex, France, and Laboratoire des Sciences de l′Environnement, ENTPE, rue Maurice Audin, 69518 Vaulx en Velin Cedex, France
We investigated the effect on soil functioning of adding leachates from municipal solid waste incinerator (MSWI) ashes to laboratory columns (bare soil) and to field experimental plots (bare soil or grass cover). Leachate of MSWI-solidified air pollution control residues (SAPCr) contained more salts but less heavy metals than did MSWIbottom ash (BA) leachate. Leachate-supplemented soils (BA soil, SAPCr soil) and control (water added) soil (W) were analyzed after 30 days. Potential denitrifying activity (PDA) and potential N2 fixation (acetylene reduction assay, ARA) were measured in controlled conditions. PDA was significantly lower in SAPCr soil than in W soil, both in the laboratory (-45%) and in bare soil in the field (-31%). ARA values were lower in bare SAPCr soil (-54%) and in bare BA (-25%) soil. Both activities remained unaffected by leachate supplementation in soil under permanent grass cover. Automated ribosomal intergenic spacer analysis (A-RISA) fingerprints and RFLP of nifH gene pools were used to assess changes in the structure of bacterial community. Multivariate analysis of these fingerprints revealed that SAPCr leachate had a stronger effect than BA leachate on the total and N2-fixing bacterial communities. Similar results were obtained for laboratory and bare soil field plots, but leachates did not affect nifH gene pools from soil under permanent grass cover. The stronger impact of SAPCr leachate on both structure of bacterial communities and activities supports the conclusion that observed effects would result from the abundance of salts rather than from heavy metal toxicity.
Introduction The quantities of solid waste materials released by human domestic activities are steadily increasing. The possibility of * Corresponding author e-mail:
[email protected]. † Ecologie Microbienne UMR CNRS 5557 Universite ´ Claude Bernard Lyon 1. ‡ Laboratoire Science du sol CISM-Universite ´ de Savoie. § Laboratoire des Sciences de l′Environnement, ENTPE. 10.1021/es025507j CCC: $22.00 Published on Web 09/28/2002
2002 American Chemical Society
reusing such waste is therefore being considered as a potential component of public environmental policies. A major concern surrounding the use of solid or solidified waste products is the potential for the release of contaminants into the environment due to contact with rain and with surface and runoff water (1). Incineration substantially reduces the volume (by about 90%) and the mass (by about 70%) of domestic solid waste and produces bottom ash (BA) and flying ash, both of which are potentially toxic due to their heavy metal and salt contents (2). Municipal solid waste incinerator (MSWI) air pollution control residues (APCr), or fly ash, contain significantly higher concentrations of cadmium, lead and zinc than does bottom ash. Both wastes contain a high concentration of soluble salts (3). APCr are enriched in metals and require specific treatment, such as solidification/stabilization with cement (4, 2) or other hydraulic binders (5), before incorporation into construction materials (6). The outdoor use of such waste materials may result in the contamination of soils by lixiviates or rainwater percolating through the waste. In most situations, solute concentrations display the following pattern in MSWI-BA: Na > Cl > K > Ca, with SO4 present at a similar molar concentration to Ca (7). The leaching of solidified/stabilized APCr (SAPCr) from construction materials also results in the release of large amounts of salt. One approach that can be used to describe and to predict the effects of such leachates on soil functioning is to assess the effects of leachates on soil bacterial communities in controlled laboratory conditions and to compare them with results obtained in field experiments. Assessment of the impact of realistic additions of MSWI ash leachates should focus on factors indicating whether leachates modify key functions or properties of soil. Shortterm changes can be assessed within a few weeks, whereas the long-term effects may still be evident 1 year after application. Leachates of MSWI-BA and MSWI-SAPCr affect the composition of the soil solution and may have consequences for the physical properties of surface soil layers and for the supply of nutrients and water to plants (8). We describe here the effects of adding MSWI-BA or -SAPCr leachates to soil on bacterial activities and community structures. We studied the following activities, which play a key role in the functioning of the soil: (i) potential denitrification, which is carried out by a large variety of soil bacteria (9) and reflects changes in soil aeration and the nitrogen cycle, and (ii) fixation of atmospheric N2, which is carried out by diazotrophs with nif genes and corresponds to the main point of entry of nitrogen into the biosphere and ecosystems (10). Techniques are available for measuring these activities in controlled and reproducible conditions, in which the potential of soil microbial communities to express these activities was optimized. Relationship between the modifications of the structure of functional communities and activities is poorly documented (11). Actually available tools to establish such a relationship are still developing. In our study, the modifications in the structure of the soil bacterial community were assessed by analyzing gene pools, using ribosomal intergenic spacer analysis (RISA) of eubacteria community (12) or restriction fragment length polymorphism (RFLP) analysis of the nifH gene pool (13).
Materials and Methods Soil and Experimental Design. Column Experiment. Sharpended PVC cylinders (ø 6 cm, h 8 cm) were used to extract VOL. 36, NO. 22, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4729
TABLE 1. Characteristics of the Studied Soil fine sands
coarse silts
loam
clays
organic matter
29
81
602
160
128
31
6.7
6.0
8.1
CaO
K2O
MgO
Na2O
Al
Cl
S
total N
C/N
2240
138
110
20
9
10
3460
1600
11
g kg-1
mg
kg-1
TABLE 2. Leachate Properties and Components pH
dry wt
Na
K
Ca
Mg
Cl-
SO42-
MSWI-BA 11 3172.5 722.5 399 119 0.025 1718 150 MSWI-SAPCr 7.6 6980 610 1000 902 nda 3680 18.5
Cu
Cr
Zn
Pb
Cd
Ni
MSWI-BA 2 0.05 0.02 0.115 0.015 MSWI-SAPCr
