Assessing Biological Toxicity of Acid Mine Drainage Using Bacterial Environmental DNA

Abstract:

Abandoned mines pose widespread environmental risk when exposed mineral surfaces lead to acid mine drainage. This is especially important considering that the United States alone has approximately 500,000 abandoned hard rock mines, many of which are not remediated, or have only temporary solutions installed. To characterize the biological toxicity of acid mine drainage-contaminated sites, conventional chemical measurements (e.g., heavy metal concentration), physical measurements (e.g., pH), and biological assays (e.g., lethal concentration for 50% death of an indicator organism or LC₅₀) are typically used. However, these methods are problematic because they cannot represent overall degree of toxicity—they fail to identify the synergistic effects of multiple biogeochemical parameters. Furthermore, conventional environmental quality biomarkers such as LC₅₀ may not be possible in strongly impacted acid mine drainage areas due to complete lethality to many biological forms. To address this problem, environmental DNA (eDNA) is becoming a critical assessment tool for contaminated sites that cannot be determined using a single biological indicator. We present a novel approach to assess biological toxicity of acid mine drainage using high-throughput 16S rDNA sequencing to evaluate bacterial community structures in different waters. Specifically, we directly compare the bacterial community structure of acid mine drainage, water, and sediment with biological toxicity of a contaminated mine site to establish a “bacterial-fingerprint” indicator of aquatic health. Because microorganisms, particularly bacteria, are involved in—and may even accelerate—the generation of acid mine drainage, bacteria are differently impacted by acid mine drainage, making bacteria an appropriate and ideal bioindicator of biological toxicity. We show that bacterial diversity can be used as an early indicator to determine the biological toxicity of fish and other aquatic life in field sites where conventional chemical, physical, or biological measurements may be insufficient.