Comments on “Degradation of 1,2,3-Trichloropropane (TCP): Hydrolysis, elimination, 
and reduction by iron and zinc” 
C. Noubactep 
Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, D - 37077 Göttingen, Germany. 
e-mail: cnoubac@gwdg.de; Tel.: +49 551 39 3191, Fax.: +49 551 399379 
 
Sarathy et al. (1) recently reported their results on the aqueous degradation of 1,2,3-
Trichloropropane (TCP) by Fe0 and Zn0. Their work is a justified attempt to support ongoing 
risk assessments of emerging contaminants in a perspective to identify methods for their 
efficient mitigation (2–5). There is a general trend to test the applicability of various 
technologies for the removal of emerging contaminants from water (4, 5). However, despite 
gaps in knowledge of the nature of metabolites, the state-of-the-art knowledge on the 
mechanism of contaminant removal by metallic iron (Fe0) suggests that filtration on Fe0 beds 
will be efficient at removing emerging contaminants and their metabolites. In fact, filtration 
on Fe0 beds has been proven efficient for the quantitative removal of various contaminants (6-
9). Accordingly, regardless on the actual removal mechanism (hydrolysis, elimination, and 
reduction), a well-designed Fe0 filter will successfully remove TCP and its metabolites from 
the aqueous phase as discussed below. 
There are three fundamental mechanisms of solute removal in porous media during fluid flow: 
(i) straining (size exclusion), (ii) adsorption (or/and deposition), and (iii) hydrodynamic 
bridging (10). The characteristic feature of Fe0 filters is the chemical reactivity of iron 
(oxidative oxidative dissolution). Therefore, beside adsorption and deposition contaminants 
can be chemically transformed (oxidized or reduced if applicable). Iron oxidative dissolution 
is volumetric expansive in nature (11). Accordingly, the initial pore volume of a Fe0 bed/filter 
is progressively occupied by voluminous hydrated ferrous/ferric oxides (HFO) which are 
further transformed to amorphous and crystalline oxides upon dehydration. Any crystalline 
oxide is at least 2.1 times larger in volume than Fe0 in the lattice structure (11). Pore filling by 
in-situ generated iron oxides is responsible for (i) porosity and permeability loss, and (ii) 
increased size exclusion capability. On the other hand, intermediate HFO are good adsorbents 
which trap contaminants in their structure during crystallization (co-precipitation). Moreover, 
continuously generated HFO can be regarded as instantaneous spider-like webs trapping 
contaminants in the porous media (12). In other words so far progressive HFO generation is 
warranted all contaminants will be removed in a well-designed Fe0 beds. Available tools to 
sustain Fe0 reactivity include bimetallics, nano-sized materials, porous Fe0-composites. 
The discussion above has not accounted for the nature of the contaminant (size, solubility, 
reactivity towards Fe0). Solely the properties of corroding Fe0 and precipitating oxides (at pH 
> 4.5) are considered. Accordingly, in Fe0 filters working at pH > 4.5, contaminants are 
basically removed by adsorption, co-precipitation, and size exclusion. Accordingly, 
understanding the impact of individual contaminants on (i) long-term Fe0 reactivity and (ii) 
system permeability is more important than understanding the actual removal mechanism. 
Given the huge number of emerging contaminants (2-5), it is not likely that the removal 
mechanism of individual contaminants will be investigated on a case-by-case basis. 
In conclusion, this discussion belittles the relevance of TCP removal mechanism (hydrolysis, 
elimination or reduction) for field Fe0 reactive walls. The test of Zn0 is intrinsically 
questioned. It is shown that contaminants are removed by Fe0 independently from their 
intrinsic characteristics. This is a strong criticism to dozens of works aiming at discussing the 
toxicity of intermediates and metabolites of some contaminants or contaminant groups in Fe0 
beds. A strong argument supporting this assertion is the efficiency of SONO arsenic filters 
(7). In SONO filters, porous Fe0-based composites primarily designated to remove arsenic 
from well waters in Bangladesh and Nepal have been shown efficient in the removal of up to 
24 other species including bacteria and viruses (7, 9). Because Fe0 are also used for 
wastewater treatment in batch systems, the study of Sarathy et al. (1) yet provides useful 
understanding of the substantial challenges confronted in studying the removal potential of 
Fe0-based systems. 
References 
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