CENSUS – Perchlorate Table

Detect and quantify bacteria responsible for biodegradation of perchlorate

Perchlorate salts are commonly used in explosives and rocket propellants as well as in industrial applications including lubricating oils, textile dye fixing, tanning, rubber manufacturing, electroplating, and paint production.  Widespread use combined with improper handling and disposal has led to widespread perchlorate contamination in the US.  Perchlorate binds weakly to soil, is extremely water soluble, and therefore is highly mobile when released into the environment.  Fortunately, some bacteria are capable of using perchlorate as a growth supporting electron acceptor producing chloride ion as an end product.  The first and often rate-limiting step in perchlorate biodegradation is the reduction of perchlorate (ClO4-) to chlorate (ClO3-) mediated by perchlorate reductase (pcrA).  Chlorate is further reduced to chlorite (ClO2-) either by perchlorate reductase or by a chlorite reductase depending on the organism.  Continued biodegradation of chlorite yields chloride ion.

Biodegradation of perchlorate is dependent upon three main factors: availability of a substrate or electron donor (carbon and energy source), in situ redox conditions, and the presence of organisms capable of perchlorate reduction.  In subsurface environments where organic carbon is low, an electron donor may have to be supplied.  The presence of competing electron acceptors (oxygen and nitrate) may also limit perchlorate reduction.

CENSUS Targets for Perchlorate

Target

MI Code

      Relevance / Data Interpretation

Perchlorate Reductase                  pcrA Quantifies the gene which catalyzes the initial, rate-limiting step in the biodegradation of perchlorate.  In some organisms, perchlorate reductase also catalyzes the reduction of chlorate to chlorite.
Denitrifying Bacteria                 DNF Under anoxic conditions, nitrate reduction can be a dominant terminal electron accepting process. The DNF assay quantifies the two types of nitrite reductase genes (nirS and nirK, respectively) encoding the second key step in denitrification.  While important in any situation where nitrate is serving as the dominant electron acceptor, quantification of denitrifying bacteria using the DNF assay can be critical at perchlorate impacted sites.  Many, but not all, perchlorate reducing bacteria will utilize nitrate as an electron acceptor potentially limiting perchlorate reduction.