Kinetic Analysis of Haloacetonitrile Stability in Drinking Waters

Haloacetonitriles (HANs) are an important class of drinking water disinfection byproducts (DBPs) that are reactive and can undergo considerable transformation on time scales relevant to system distribution (i.e., from a few hours to a week or more). The stability of seven mono-, di-, and trihaloacetonitriles was examined under a variety of conditions including different pH levels and disinfectant doses that are typical of drinking water distribution systems. Results indicated that hydroxide, hypochlorite, and their protonated forms could react with HANs via nucleophilic attack on the nitrile carbon, forming the corresponding haloacetamides (HAMs) and haloacetic acids (HAAs) as major reaction intermediates and end products. Other stable intermediate products, such as the <i>N</i>-<i>chloro</i>-haloacetamides (<i>N</i>-<i>chloro</i>-HAMs), may form during the course of HAN chlorination. A scheme of pathways for the HAN reactions was proposed, and the rate constants for individual reactions were estimated. Under slightly basic conditions, hydroxide and hypochlorite are primary reactants and their associated second-order reaction rate constants were estimated to be 6 to 9 orders of magnitude higher than those of their protonated conjugates (i.e., neutral water and hypochlorous acid), which are much weaker but more predominant nucleophiles at neutral and acidic pHs. Developed using the estimated reaction rate constants, the linear free energy relationships (LFERs) summarized the nucleophilic nature of HAN reactions and demonstrated an activating effect of the electron withdrawing halogens on nitrile reactivity, leading to decreasing HAN stability with increasing degree of halogenation of the substituents, while subsequent shift from chlorine to bromine atoms has a contrary stabilizing effect on HANs. The chemical kinetic model together with the reaction rate constants that were determined in this work can be used for quantitative predictions of HAN concentrations depending on pH and free chlorine contact times (CTs), which can be applied as an informative tool by drinking water treatment and system management engineers to better control these emerging nitrogenous DBPs, and can also be significant in making regulatory decisions

Formation and Occurrence of <i>N‑Chloro</i>-2,2-dichloroacetamide, a Previously Overlooked Nitrogenous Disinfection Byproduct in Chlorinated Drinking Waters

Haloacetamides (HAMs) are a class of newly identified nitrogenous disinfection byproducts (N-DBPs) whose occurrence in drinking waters has recently been reported in several DBP surveys. As the most prominent HAM species, it is commonly acknowledged that 2,2-dichloroacetamide (DCAM) is mainly generated from dichloroacetonitrile (DCAN) hydrolysis because the concentrations of these two compounds are often well correlated. Instead of DCAM, a previously unreported N-DBP, <i>N</i>-<i>chloro</i>-2,2-dichloroacetamide (<i>N-Cl</i>-DCAM), was confirmed in this study as the actual DCAN degradation product in chlorinated drinking waters. It is suspected that <i>N-Cl</i>-DCAM has been erroneously identified as DCAM, because its nitrogen-bound chlorine is readily reduced by most commonly used quenching agents. This hypothesis is supported by kinetic studies that indicate almost instantaneous <i>N</i>-chlorination of DCAM even at low chlorine residuals. Therefore, it is unlikely that DCAM can persist as a long-lived DCAN decomposition product in systems using free chlorine as a residual disinfectant. Instead, chlorination of DCAM will lead to the formation of an equal amount of <i>N-Cl</i>-DCAM by forming a hydrogen bond between hypochlorite oxygen and amino hydrogen. Alternatively, <i>N-Cl</i>-DCAM can be produced directly from DCAN chlorination via nucleophilic addition of hypochlorite on the nitrile carbon. Due to its relatively low p<i>K</i>_a value, <i>N-Cl</i>-DCAM tends to deprotonate under typical drinking water pH conditions, and the anionic form of <i>N-Cl</i>-DCAM was found to be very stable in the absence of chlorine. <i>N-Cl</i>-DCAM can, however, undergo acid-catalyzed decomposition to form the corresponding dichloroacetic acid (DCAA) when chlorine is present, although those acidic conditions that favor <i>N-Cl</i>-DCAM degradation are generally atypical for finished drinking waters. For these reasons, <i>N-Cl</i>-DCAM is predicted to have very long half-lives in most distribution systems that use free chlorine. Furthermore, an analytical method using ultra performance liquid chromatography (UPLC)/negative electrospray ionization (ESI^–)/quadrupole time-of-flight mass spectrometry (qTOF) was developed for the detection of a family of seven <i>N-chloro</i>-haloacetamides (<i>N-Cl</i>-HAMs). Combined with solid phase extraction (SPE), the occurrence of <i>N-Cl</i>-DCAM and its two brominated analogues (i.e., <i>N-chloro</i>-2,2-bromochloroacetamide and <i>N-chloro</i>-2,2-dibromoacetamide) was quantitatively determined for the first time in 11 real tap water samples. The discovery of <i>N-Cl</i>-DCAM or, more broadly speaking, <i>N-Cl</i>-HAMs in chlorinated drinking waters is of significance because they are organic chloramines, a family of compounds that is perceived to be more toxicologically potent than halonitriles (e.g., DCAN) and haloamides (e.g., DCAM), and therefore they may pose greater risks to drinking water consumers given their widespread occurrence and high stability

<i>Penicillium fusisporum</i> and <i>P. zhuangii</i>, Two New Monoverticillate Species with Apical-Swelling Stipes of Section <i>Aspergilloides</i> Isolated from Plant Leaves in China

<div><p>Two new <i>Penicillium</i> species isolated from plant leaves are reported here, namely, <i>P. fusisporum</i> (type strain AS3.15338^T = NRRL 62805^T = CBS 137463^T) and <i>P. zhuangii</i> (type strain AS3.15341^T = NRRL 62806^T = CBS 137464^T). <i>P. fusisporum</i> is characterized by fast growth rate, apical-swelling monoverticillate penicilli, verrucose stipes, fusiform to oblong conidia about 3.5–4×2–2.5 µm and cinnamon-colored sclerotia. While <i>P. zhuangii</i> presents a moderate growth rate, it also bears apical-swelling monoverticillate penicilli but its stipes are smooth-walled, and produces ovoid to globose smooth-walled conidia about 3–3.5 µm. Both species belong to section <i>Aspergilloides</i>, and <i>P. fusisporum</i> is related to “<i>P. thomii</i> var. <i>flavescens</i>”, while <i>P. zhuangii</i> is morphologically similar to <i>P. lividum</i>. Phylogenetic analyses of sequences of calmodulin and beta-tubulin genes both show that the two new taxa form distinct monophyletic clades.</p></div

Bayesian Inference of Reticulate Phylogenies under the Multispecies Network Coalescent

<div><p>The multispecies coalescent (MSC) is a statistical framework that models how gene genealogies grow within the branches of a species tree. The field of computational phylogenetics has witnessed an explosion in the development of methods for species tree inference under MSC, owing mainly to the accumulating evidence of incomplete lineage sorting in phylogenomic analyses. However, the evolutionary history of a set of genomes, or species, could be reticulate due to the occurrence of evolutionary processes such as hybridization or horizontal gene transfer. We report on a novel method for Bayesian inference of genome and species phylogenies under the multispecies network coalescent (MSNC). This framework models gene evolution within the branches of a phylogenetic network, thus incorporating reticulate evolutionary processes, such as hybridization, in addition to incomplete lineage sorting. As phylogenetic networks with different numbers of reticulation events correspond to points of different dimensions in the space of models, we devise a reversible-jump Markov chain Monte Carlo (RJMCMC) technique for sampling the posterior distribution of phylogenetic networks under MSNC. We implemented the methods in the publicly available, open-source software package PhyloNet and studied their performance on simulated and biological data. The work extends the reach of Bayesian inference to phylogenetic networks and enables new evolutionary analyses that account for reticulation.</p></div

PGENETICS-D-15-02479R1-DATA

This directory contains four input files on which PhyloNet can be run to conduct the Bayesian analyses reported in the paper for the four data sets (the wheat data set, the mouse data set, the mosquito autosome data set, and the mosquito X chromosome data set)

Runoff losses under different micro-patterns of BSCs.

<p>(Note: FUCC pattern, Scattered pattern, UCLN pattern and UNLC pattern refers to fully-covered BSCs pattern, scattered BSCs pattern with 50% BSC coverage, upper half BSCs with lower half non-crusted bare soil pattern, and upper half non-crusted bare soil with lower half BSCs pattern, respectively.)</p

Phylogenetic history of the bread wheat.

<p>(<b>A</b>–<b>C</b>) The three phylogenetic networks that comprise the 95% credible set, (<b>D</b>) and a plausible summary of the three networks that is consistent with the model of phylogenetic history of bread wheat (Fig 3 in [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006006#pgen.1006006.ref029" target="_blank">29</a>]).</p

Soil anti-scourability under BSCs and non-BSCs conditions.

<p>Soil anti-scourability under BSCs and non-BSCs conditions.</p

Analysis results for the six phylogenies in Figure 2 using gene tree topologies inferred by maximum parsimony (using PAUP*).

<p>Analysis results for the six phylogenies in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002660#pgen-1002660-g002" target="_blank">Figure 2</a> using gene tree topologies inferred by maximum parsimony (using PAUP*).</p

Colonies of <i>P. zhuangii</i> AS3.15341 ^T incubated 7 d at 25°C.

<p>A, Cz; B, CYA; C, MEA; D, YES.</p