MR-1 oxidatively degrades substances, including metals, in an aerobic setting, through an advanced oxidation process (AOP) called the microbially driven Fenton reaction [38,237]. This process has a significant impact on As behaviour, particularly in the As(V)-bearing Fe(III) mineral system. In the reaction, a continuous supply of O 2 and Fe(II) is required, and to compliment this requirement, this species can continuously reduce Fe(III) to Fe(II) [15]. Apart from O 2 , the bacterium can also utilise NO 2 − , NO 3 − , S 2 O 3 2− , S o , DMSO, and fumarate as terminal electron acceptors for respiration [140]. In Fenton's reaction, H 2 O 2 is produced due to the addition of O 2 [238]. Subsequently, the already liberated Fe(II) reacts with the generated H 2 O 2 to form the hydroxyl radical (HO • ) and hydroxyl ions (OH − ). The former is significant in metal decomposition and biogeochemical cycling, including As [239][240][241]. This distinguishing feature is one of the attributes allowing MR-1 to play an indispensable role in the decomposition of environmental pollutants, including heavy metals. The overview of the Fenton reaction is represented in the chemical equations below.
Fenton reaction describes the formation of Fe 2+ and hydroxyl radicals due to the coexistence of hydrogen peroxide H 2 O 2 and Fe 3+ [237]. Further reaction of Fe 2+ and H 2 O 2 produces OHand more hydroxyl radicals HO • [238]. The HO • serves as an important component for the degradation of As and other contaminants.

### Language ###
English

### Assessment ###
We could ask about what is produced during Fenton's reaction that helps break down metals and pollutants.

### Query ###
What chemical compound does Fenton's reaction produce that helps degrade metals?
What chemical compound does Fenton's reaction produce that helps degrade metals?