“Nature and Estimated Human Toxicity of Polar Metabolite Mixtures in Groundwater Quantified as TPHd/DRO at Biodegrading Fuel Release Sites,”

Examining the Extraction Efficiency of Petroleum‐Derived Dissolved Organic Matter in Contaminated Groundwater Plumes

“…Zemo et al (, ) argued on the basis of 760 tentatively identified degradation intermediates identified by Mohler et al () that the intermediates pose little to no risk in groundwater, but the issue remains controversial (Mohler et al. ; Brewer and Hellmann‐Blumberg ; ITRC ). The dissolved organic plume is of interest because it acts as a conduit to mobilize compounds derived at the petroleum source to downgradient receptors such as drinking water supplies and surface waters (Bekins et al ; Mackay et al ).…”

Biological Effects of Hydrocarbon Degradation Intermediates: Is the Total Petroleum Hydrocarbon Analytical Method Adequate for Risk Assessment?

“…The first method is problematic because it assumes that degradation intermediates have the same toxicity as parent compounds and are present at the same concentrations, even though they have different properties. Moreover, recent studies have found greater toxicity in PAH degradation products than for the parent hydrocarbons. , The second method is limited because it assumes toxicity factors for single compounds are adequate to represent a class of compounds . More importantly, it is based on the fraction that is extracted with DCM (DCM-total), which recovers one-third or less of the degradation intermediates present at this site.…”

“…Potential hazards and/or risks posed by degradation intermediates of petroleum hydrocarbons to human health and ecological receptor communities have been the focus of several studies. − Some conclude that the risk is low; − but a number of publications present evidence that the risks of petroleum hydrocarbon intermediate degradation products to humans or ecological receptors may be greater than anticipated and in need of further characterization. − For example, two studies of bioremediation of polyaromatic hydrocarbons (PAHs) found greater toxicity associated with hydroxylated and carboxylated transformation products than with the parent PAHs. , One aspect of the issue concerns regulatory policy on the appropriate use of analytical methods to quantify total petroleum hydrocarbons (TPH) in water. , Some methods include degradation intermediates and other methods exclude these classes from quantifications and exposure assessments.…”

Toxicity of polar metabolites associated with petroleum hydrocarbon biodegradation in groundwater

“…Of particular interest regarding adverse effects in humans are esters 16 and 17 in the bottom row of Figure 1. They are labeled 1,2-benzenedicarboxylic acid, mono(2-ethylhexyl)ester, and 1,2-benzenedicarboxylic acid, bis (2-methylpropyl)ester but they are better known as mono(2-ethylhexyl) phthalate (MEHP) and diisobutylphthalate, respectively.…”

“…In contrast, assuming that complex mixtures of largely unknown and uncharacterized metabolites are not toxic would not provide adequate protection. Thus, regulators recommend against routine use of silica gel cleanup . The comparison of duplicate groundwater samples processed with and without silica gel cleanup can be useful for site characterization and to assess the degree to which natural degradation is taking place, but data from samples processed with silica gel cleanup are not appropriate for risk assessments or comparison with risk‐based screening levels.…”