08 Apr Fires, Toxins, & Other Unintended Consequences

Fires, Toxins, & Other Unintended Consequences

The thin glass teardrop in the picture contains approximately 750 ml of carbon tetrachloride (CT), which has discolored over time. As recently as the 1960s, these teardrops were suspended at the ceiling in plastic netting. In the event of a fire, the plastic melted and released the teardrops. Once broken, the CT is not flammable, and the vapors are very dense, so the CT smothers the flames. Good, right?

Remediation is often the effort to address unintended consequences. When heated, CT decomposes to extremely toxic phosgene and hydrogen chloride. When ZVI is used to remediate CT, the remediation typically stalls at methylene chloride (MC).

I’ve written a few times that BOS 100® is not simply zerovalent iron (ZVI) and activated carbon but that the elemental iron is integral to the carbon’s molecular structure. When a chemical interacts with BOS 100, the resulting reaction is often unique and beyond that of ZVI. CAT 100 raises the bar by supporting BOS 100 with biodegradation—two broad degradation pathways from one product.

While the following graphs focus on carbon tetrachloride (CT) and its degradation products, chloroform (CF) and methylene chloride (MC), this data is illustrative of data RPI has for similar constituents found in comingled plumes such as 1,2 dichloroethane (ethylene dichloride). These CT results are from a bench test using CAT 100, but BOS 100 has also successfully remediated CT sites. See, for example, Rosansky (2019). The media in the bench test is groundwater from a site contaminated with CT, CF, and MC. The values reported are the average of five analyses.

Figure 1. shows 551 ppm of CT at day zero. By day 65, the CT is non-detect at 0.5 ppb. So, where did the CT go?

Figure 1.

The next stage in the CT degradation pathway leads to CF. The total CF comes from the groundwater used in the bench study (65.4 ppm) plus the CT degraded to CF; thus, 428 ppm of CF would be generated, and 65.4 ppm would come from the bench test water. In total, there could be 493 ppm of CF. As you can see, only 155 ppm of CF remained after 65 days.

The reaction may be bogged down at MC. If the 551 ppm of CT were completely degraded to MC, we’d have 307 ppm of MC. At the 60 days, the MC was just 8.46 ppm, of which 1.74 ppm was initially present in the groundwater used for the bench test, so very little CT remains as MC.

I selected a miserably tedious way to make this point: CT is not stalling in the degradation path to CO₂ and methane, which differs from ZVI. The literature indicates that CF reduction with ZVI is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. CT degradation typically stalls at methylene chloride.

A more direct approach to viewing the degradation of the chlorinated contaminants and their fate in the bench study may be found in examining chloride generation. In Figure 2, the chloride levels in the control are flat over 60 days. The orange graph line is BOS 100, and chloride generation is evident. The blue graph line is CAT 100. The chloride generated by CAT 100 represents 78% of the total chloride that could theoretically be produced—not too bad for only 60 days.

Figure 2.

At RPI, we’ve examined many contaminants and their degradation on CAT 100. From these studies, we understand that CAT 100 can degrade anything ZVI can degrade, and many contaminants ZVI cannot degrade or does so poorly, such as CT. If you have a contaminant or soup of contaminants and you’d like to see if CAT 100 could help you, give us a call or fill out or site evaluation form.

Rosansky, D. N. (2019). In Situ Activated Carbon Case Study Review. Port Hueneme, CA: Naval Facilities Engineering Command NAVFAC.

Kind Regards,

Ed Winner, PhD, Vice President
Remediation Products, Inc.