AsIII

AsIII denotes arsenic in the +3 oxidation state, commonly referred to as arsenite in inorganic chemistry. In aqueous solution, the principal arsenite species are arsenous acid, H3AsO3, and its conjugate bases H2AsO3^- and HAsO3^2-, with H3AsO3 predominating at lower pH and deprotonation increasing with pH (pKa values are generally around 9–12 for the successive steps). These speciation changes influence reactivity, mobility, and bioavailability in environmental contexts.

Environment and reactivity of AsIII are driven by redox conditions. In natural waters, AsIII is stable under reducing conditions, while oxidation to AsV occurs in more oxidizing environments. Arsenite species tend to interact with mineral surfaces and are generally more soluble under reducing conditions, affecting groundwater transport and contamination risk. By contrast, arsenate (AsV) species dominate under oxidizing conditions. The interconversion between AsIII and AsV is important for biogeochemical cycling and for designing effective water treatment strategies.

Toxicology and health effects are central to AsIII significance. Inorganic arsenite compounds are highly toxic, primarily because they bind to sulfhydryl groups in enzymes, disrupting energy metabolism and other cellular functions. Chronic exposure is associated with skin lesions, cardiovascular and neurovascular effects, and an elevated cancer risk. Because AsIII is typically more toxic and more readily taken up by organisms than AsV, distinguishing arsenite from arsenate is important in risk assessment and remediation.

Applications and regulation: Arsenic trioxide (As2O3) is used medicine for certain leukemias, notably acute promyelocytic leukemia, under controlled medical supervision. Historically, arsenic compounds have been used as pesticides and wood preservatives. Regulatory limits for arsenic in drinking water emphasize total arsenic and often require speciation analyses to distinguish AsIII from AsV for health risk evaluation and treatment design.