Age-dating Chemical Contamination Flashcards
Why is age dating chemical contamination is important?
Environmental forensic scientists are often asked to determine the age and/or release date of contaminants found in groundwater, soils, and sediments.
How is age dating chemical contamination made possible
Chemical contamination age-dating is made possible by a variety of scientific tools that can be combined to generate a multi-line of evidence approach to a specific release.
Age Dating requires
- that there be some inherent property of the released chemical that will change over time at a reasonably predictable rate and can therefore be used as a “clock,” that the matrix in which the chemical is found (e.g., sediments) can itself be dated,
- or that some change in manufacture of the chemical can serve as a historical “time stamp.”
- Chemical forensic techniques alone do not usually make absolute dating possible, but they can, in the hands of knowledgeable and careful experts, allow estimation of timing
Qualities that change throughout time and can be used to determine age
Chemical changes caused by radioactive decay
Chemical changes caused by abiotic processes such as hydrolysis
Chemical changes caused by biodegradation and other weathering processes
Growth in groundwater plume length
Changes over time in manufacturing processes and the use of additives.
Why is Carbon 14 used?
Carbon 14 is an isotope that is unstable and decay at a predictable rate. As a result it is used to date organic materials as far back as about 60,000 years and to distinguish “dead carbon” sources from recent biomass sources.
What is dead carbon?
no 14C remaining.
What is geochronology and how does help in age dating?
The application of radioisotopes, specifically 210 Pb, is
to date sediments and the contaminants associated with
sediments.
Why is uranium decay process is useful in dating sediments?
Uranium-containing rocks produce radon gas, which decays and falls out and washed into water bodies to form 210Pb, which has a half life of 22.3 years, making it useful for dating sediments over the past 150 years.
What is geochronology and how does help in age dating?
The application of radioisotopes, specifically 210 Pb, is
to date sediments and the contaminants associated with
sediments.
How is Cesium-137 is used in age dating?
Cesium-137, which is a uranium fission product mainly from atmospheric nuclear testing. 137Cs is often used as a second independent method to age- date contaminants in sediments.
How is tritium used to age date?
The radioactive isotope tritium,
also produced in nuclear explosions, can be used to age-date groundwater.
What are the types of changes a chemicals undergoes when released?
Biotic and Abiotic
What is a biotic transformation?
Biotic transformations involve microorganisms and biodegradation.
What is abiotic transformation?
Abiotic transformations do not involve microorganisms, as
when the chlorinated solvent 1,1,1-trichloroethane (TCA),
breaks down (hydrolyzes) in the presence of water to form 1,1-
dichloroethene (DCE).
