Few studies have elucidated the agent(s) that generate iodinated disinfection byproducts during drinking water treatment. We present a kinetic investigation of iodination of dimethenamid (DM), a model compound lacking acid− base speciation. Water chemistry parameters (pH, [Cl − ], [Br − ], [I − ], and [pH buffer]) were systematically varied. As pH increased (4−9), DM iodination rate decreased. Conventional wisdom considers hypoiodous acid (HOI) as the predominant iodinating agent; nevertheless, HOI (pK HOI = 10.4) could not have produced this result, as its concentration is essentially invariant from pH 4−9. In contrast, [H 2 OI + ] and [ICl] both decrease as pH increases. To distinguish their contributions to DM iodination, [Cl − ] was added at constant pH and ionic strength. Although chloride addition did increase the iodination rate, the reaction order in [Cl − ] was fractional (≤0.36). The contribution of ICl to DM iodination remained below 47% under typical drinking water conditions ([Cl − ] ≤ 250 mg/L), implicating H 2 OI + as the predominant iodinating agent. Distinctions between DM iodination versus chlorination or bromination include a more pronounced role for the hypohalous acidium ion (H 2 OX + ), negligible contributions by hypohalous acid and molecular halogen (X 2 ), and a more muted influence of XCl, leading to lesser susceptibility to catalysis by chloride.

Halogenation and oxidation of organic matter in chlorinated and chloraminated water are typically attributed to the most abundant electrophiles present. This interpretation sometimes fails to explain laboratory observations, including halogenation kinetics and product distributions. Exotic electrophiles, species commonly overlooked in the environmental literature, can help to resolve these discrepancies. Herein, we review evidence demonstrating the significance of lesser-studied electrophilic chlorinating (Cl2 and Cl2O), brominating (BrCl, BrOCl, and Br2O), and iodinating (H2OI+ and ICl) agents in chlor­(am)­inated water. The evidence includes reaction rate dependencies on [Cl–], [H+], and [HOCl] that cannot be attributed to the reactivity of hypohalous acids or hypohalites alone. For example, enhancement of chlorination and bromination rates by Cl– implicates Cl2 and BrCl, respectively, as active halogenating agents. Herein, we discuss a new method for quantifying the sensitivity of halogenation to rate enhancement by Cl–. We also discuss complexities that Cl– can impart on iodination kinetics. In addition, we highlight recent insights into radical-mediated reaction pathways and unexpected organic electrophiles in chlorinated water. Finally, we discuss practical implications, identify research needs, and offer recommendations to improve the design of future halogenation experiments. Overall, this review aims to spur new research into underappreciated electrophiles in chlor­(am)­inated water.

regular income support to low-income households, access to testing and shelter among the homeless, and improving health-care access in low-income neighbourhoods have the potential to dramatically reduce future pandemic morbidity and mortality, perhaps even more so among individuals with respiratory conditions such as asthma. 7 More broadly, the effects of COVID-19 have shed light on the broad disparities within our society and provides an opportunity to address those disparities moving forward.

We trace the evolutionary correlation between stress resistance and longevity in populations of Drosophila melanogaster selected for stress resistance over many generations. Females selected for desiccation resistance and both females and males selected for increasing starvation resistance initially show concurrent increases in longevity, but then begin to decrease in longevity, even as stress resistance continues to increase. We demonstrate that the correlation between two fitness traits can change and that this change is due to sustained selection rather than a genotype-by-environment interaction or inbreeding depression. The breakdown in evolutionary correlation we report underscores the difficulty of extrapolating the results from short-term selection experiments to predictions of longterm evolution.