Insights into the formation and mitigation of iodinated disinfection by-products during household cooking with Laminaria japonica (Haidai)

Highlights

• Health risk of I-DBP exposure from household cooking with Haidai was overlooked.

• I-DBPs formed from simulated household cooking with Haidai reached to mg/L level.

• Factors affecting I-DBP formation from household cooking with Haidai were ascertained.

• The high temperature of cooking played a decisive role in facilitating I-DBP formation.

• The soak of Haidai before cooking for food preparation inhibited I-DBP formation.

Abstract

Iodinated disinfection by-products (I-DBPs) have attracted extensive interests because of their higher cytotoxicity and genotoxicity than their chlorinated and brominated analogues. Our recent studies have firstly demonstrated that cooking with seaweed salt could enhance the formation of I-DBPs with several tens of μg/L level. Here, I-DBP formation and mitigation from the reaction of disinfectant with Laminaria japonica (Haidai), an edible seaweed with highest iodine content, upon simulated household cooking process was systematically investigated. The total iodine content in Haidai ranged from 4.6 mg-I/g-Haidai to 10.0 mg-I/g-Haidai, and more than 90% of iodine is soluble iodide. During simulated cooking, the presence of disinfectant simultaneously decreased iodide by 15.0–32.8% to 2.7–5.8 mg/L and increased total organic iodine by 1.3–10.9 times to 0.5–1.8 mg/L in Haidai soup, proving I-DBP formation. The concentrations of iodinated trihalomethanes and haloacetic acids were at the levels of several hundreds of μg/L and several μg/L, respectively, which are 2–3 orders and 1–2 orders of magnitude more than those in drinking water. Effects of key factors including disinfectant specie, disinfectant dose, temperature and time on I-DBP formation were also ascertained, and temperature and disinfectant specie played a decisive role in the formation and speciation of I-DBPs. In order to avoid the potential health risk from the exposure of I-DBPs in Haidai soup, it is prerequisite to soak and wash dry Haidai sample over 30.0 min before cooking, which could effectively remove major soluble iodide. In general, this study provided the new insight into I-DBP formation from daily household cooking with Haidai and the corresponding enlightenment for inhabitants to eat Haidai in daily life.

Introduction

Disinfection is an important composition of drinking water treatment process due to its effective inactivation of water-borne pathogens (Plewa et al., 2004; Rosario-Ortiz et al., 2016). However, the commonly used chlorine-containing disinfectants such as chlorine and chloramines can react with naturally occurring organic matter, anthropogenic contaminants, and halides to produce unwanted halogenated disinfection by-products (DBPs) (Zhou et al., 2015; Liu et al., 2018; Yang et al., 2018; Ding et al., 2019a; Simpson and Mitch, 2021). Among these halogenated DBPs, the toxicity of iodinated DBPs (I-DBPs) is several orders of magnitude greater than chlorinated and brominated analogues owing to the higher bond length of alkyl iodide and leaving tendency of iodine in SN₂ reaction (Richardson et al., 2008; Wagner and Plewa, 2017). Iodinated trihalomethanes (I-THMs) are several times more cytotoxic in Chinese hamster ovary (CHO) cells than their chlorinated and brominated analogues (Wagner and Plewa, 2017). Hanigan et al. (2017) found that monoiodoacetic acid (MIAA) had developmental toxicity to Zebrafish embryo at low concentrations (100.0 μM), while monochloroacetic acid (MCAA) and monobromoacetic acid (MBAA) did not exhibit developmental toxicity even at the concentration up to 500.0 μM . The mutagenicity of MIAA to CHO cells was 2.6 times and 523.3 times higher than that of MBAA and MCAA, respectively (Richardson et al., 2007), while the cytotoxicity of MIAA to Salmonella typhimurium was 2.9 times and 53.5 times higher than that of MBAA and MCAA, respectively (Plewa et al., 2004).

Although I-DBPs have higher toxicity than their chlorinated and brominated counterparts, I-DBP concentrations in finished water, which are several orders of magnitude lower than their chlorinated and brominated analogues, are generally at a level of several tens ng/L–several μg/L (Fuge and Johnson, 1986; Dong et al., 2019; Yang et al., 2019; Lau et al., 2020). The lower I-DBP level in finished water is attributed to the lower concentration of iodine source, which could be divided into three categories: iodide, iodate and iodinated organic compound (Hu et al., 2018; Postigo et al., 2018). It was previously reported that iodide, iodate, and iodinated organic matter concentration in source water, which are dependent on geologic dissolution, seawater intrusion, and human activities, ranged from < 0.5 μg/L to 200.0 μg/L, from < 0.5 μg/L to 3.4 μg/L, and from < limits of detection to 100.0 μg/L, respectively, and the total iodine (TI) content of source water was generally below than 10.0 μg/L (Dong et al., 2019). Given that DBP-associated toxicity is dependent on both concentration of specific DBPs and its toxic potency, the contributions of I-DBPs to overall DBP-associated toxicity are determined by the concentration of iodine in source water to some extent (Dong et al., 2017). The trace iodine level, at which they generally occur in source water, indicates that I-DBPs might be relatively unimportant contributors to overall DBP-associated toxicity under certain condition (Hu et al., 2018; Lau et al., 2020). In addition to iodine derived from source water, iodine derived from food can also serve as iodine source of I-DBPs (Becalski et al., 2006; Zhang et al., 2020). To deal with health problems caused by iodine deficiency, many countries promulgated documents, of which the addition of iodine in edible salt as supplement was stipulated (MPHC, 2011). The dominant iodine specie for iodine enhancers in commercial iodized salt is iodate rather than iodide owing to its chemical stability (Yan et al., 2016). As a result, household cooking with commercial iodized salts could slightly enhance the formation of I-DBPs with a concentration up to ∼ 20.0 μg/L (Becalski et al., 2006; Yan et al., 2016). Moreover, previous studies have identified several aromatic DBPs with higher toxic potency in boiling/cooking samples (Pan et al., 2016; Zhang et al., 2020).

Our recent study found that I-THMs and total organic iodine (TOI) upon simulated household cooking with seaweed salt and tap water reached the levels of several tens μg/L (Cao et al., 2022; Qu et al., 2022). Moreover, the toxicity of tap water after simulated household cooking with the addition of seaweed salt was several orders higher than that without the addition of seaweed salt. This phenomenon can be explained by the fact that the iodine species of seaweed salt are different from those of widely edible iodi (Zhang et al., 2020) zed salt. The iodine in seaweed salt is extracted from natural iodine-rich marine products (e.g. Laminaria japonica [Haidai], Porphyra umbilicalis, Undaria pinnatifida), of which the dominant iodine species are iodide and organic iodine (Doh et al., 2018). Among these seaweeds, Haidai has the highest TI content (Hou et al., 1997). It was reported that TI content in Haidai is generally around 0.3% of the dry weight, and the highest can reach 0.7%–0.9%, which is far higher than that in surface water (10–20 μg/L). Given that Haidai is also the commonly edible marine product in Asian countries, the iodine leached from Haidai during household cooking might react with residual disinfectant in tap water to form unwanted I-DBPs. To our knowledge, there was no similar research on the I-DBP formation from edible seaweed during household cooking. Moreover, the reaction scenarios of drinking water disinfection for I-DBP formation are obviously different from those of household cooking (Chen et al., 2021). For example, the reaction temperature of household cooking is substantially higher than that of drinking water disinfection, whereas the reaction time and disinfectant dose of household cooking process are much lower than those of drinking water disinfection (Liu and Reckhow, 2015). Accordingly, the features of I-DBP formation upon household cooking might be different from those upon drinking water disinfection (Zhou et al., 2014). Besides, a certain amount of processing for Haidai sample (e.g., soak and wash) before cooking is required, which might also affect I-DBP formation during cooking. These have stimulated us to investigate the I-DBP formation from Haidai during simulated household cooking.

Therefore, the purpose of this paper was to study the I-DBP formation from Haidai during simulated household cooking. Moreover, the effects of various key factors (reaction temperature, reaction time, disinfectant specie and disinfectant dose) and food pretreatment (soak time) on I-DBP formation were also investigated.