Microbial Activity in Arsenic Contaminated Soil

Samantha Wolf, Mark Emerson, Derek Laskowsky

Hypothesis

Will soil previously contaminated with CCA contain microbes that show more resilience to prolonged exposure to CCA wood than microbes in an uncontaminated soil?

Introduction

The purpose of CCA is to prevent rot and damage to lumber from termites, effectively acting as a pesticide, in addition to strengthening the lumber.

During the 1940’s the lumber industry began its large-scale treatment of lumber with chromated copper arsenate (CCA) for preservation.

Introduction Cont.

The complications brought on by the CCA treated lumber is the leaching of chromated copper arsenate into the surrounding soil.

The focus of this study is to determine if CCA exposed microbes are resilient to the CCA, compared to non-CCA exposed microbes.

Methods: Soil sampling and analysis Soil samples from 3”, 6”, and 9”

from CCA contaminated site.

Soil sample and analysis

Metal Concentrations

Sample at 3”: Arsenic at 63.5

ppm cadmium at 2.2

ppm chromium at 31

ppm copper at 44 ppm

Average concentrations:

Arsenic 6.5 ppm cadmium at 0.1 -

1.0 ppm chromium at 70

ppm copper at 20 ppm

Microbial Enrichment

Brain-heart nutrient broth in shaker incubator for 1 week.

Control, CCA Soil, Control soil with 2.2g CCA wood, CCA Soil with 2.2g CCA wood.

Colony Forming Units

Plated on agar, incubated for 24 hrs.

Counted and extrapolated to 10^4

CFU Count

0

50000

100000

150000

200000

250000

300000

350000

400000

Colony count per sample

Results

All results are per .5ml

Bact

eria

Col

onie

s

Conclusion

The CFU count was highest in the CCA soil sample inoculated with the CCA wood chip. The microbes in the soil must be conditioned to presence of arsenic.

Arsenic loving microbes.