A critical analysis of potential formation and health risk of disinfection by products in drinking water

The reaction between chlorine and organic matter in water treatment processes formed a new product called disinfection by products (DBPs). Natural organic matter is the main precursor of the DBPs formation. Trihalomethanes as the most found DBPs in drinking water and N-Nitrosamine as one of kind DBPs from contaminated water. Those compounds are predicted to be carcinogenic for human being. This critical analysis goal is to investigate the potential formation of DBPs in water treatment and analysis the potential health risk to find the best strategies for reducing the DBPs formation. It presents a comprehensive literature review of research to understand the formation of DBPs especially Trihalomethanes and N-Nitrosamine in water treatment. Then investigation the health risk potential of trihalomethanes an N-Nitrosamine. Trihalomethanes always formed during the disinfection process. Trihalomethanes have the high can endanger human health because of the potential of cytotoxicity, genotoxicity, and lead to toxicity. N-Nitrosamine generally come in a lower concentration than Trihalomethanes but give higher health risk. Establish DBPs concentration limits is very important to protect the health of humans who consume water. Prevention of the formation of DBPs compounds by removing organic precursors in the water and adding advanced treatment after the disinfection process.


Introduction
Disinfection is a main step in drinking water treatment for inactivation the pathogen microorganism.Chlorination is the most used disinfection agent (disinfectant) in the world because it effective to inactivate pathogenic microorganisms and low in price.However, the harmful compound is generated during the process and produced disinfection by-products (DBPs) because of the reactions between organic matter and chlorine [1].DBPs has human health risk because its harmful compound in water drinking so that the water companies have to put serious attention with their occurrence in raw water sources [2].The number and concentration of DBPs depend on the presence and variety of organic 1239 (2023) 012027 IOP Publishing doi:10.1088/1755-1315/1239/1/012027 2 matter in the water naturally such as natural organic matter (NOM) and also dissolved matter such as dissolved organic matter (DOM).
NOM is the most precursor of DBPs together with the compound from pharmaceuticals, pesticides, detergents, textile dyes as the anthropogenic contaminants, bromide and iodide compounds, effluent of wastewater discharges, and drinking water treatment operational parameters (such as type of disinfectant, dosage, pH, reaction time and temperature) may affect the formation of DBPs [2].NOM presence in lake, stream, and water surface is derived from organic compound of biotic and abiotic processes such as soils and plants, algae and the growth of bacterial in water [3].NOM is counts as dissolved matter which is commonly measured as dissolved organic carbon (DOC) and UV absorbance at 254 nm (UV254).
DOM in source water mostly originates from ecological impacts and human activities at the specific location.A conventional water treatment process including coagulation, sedimentation, and filtration slightly removes DOM.A certain amount of DOM, therefore, can pass through a conventional process.Health risks may arise from the consumption of water contaminated with DOM and its DBPs.
Disinfection process generates the variety of DBPs compounds such as trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), halophenols and halopropanoles [2,4].Some of DBPs such as THMs, HAAs has been regulated by international regulation of USEPA and WHO due to the consideration of high risk on human health.However, there are still unregulated DBPs that unknown and presence in very low concentration but they can be more toxic and high risk for the human health as cancer or other genotoxic diseases [2,5].
Discharge of wastewater can be source of DBPs precursor in the surface water [6].There are no specific regulations related to wastewater treatment (WWT) effluent for the formation of DBPs, so potential disturbance of natural organism and human health are increase.Effluent of WWT has big contribution of Nitrogenous-DBPs (N-DBPs) formation because rich of nitrogen (ammoniac, organic nitrogen such as amino acids, peptides) [7].Although N-DBP presence in very low concentration compare to regulated DBPs (THM dan HAA), N-DBP has higher health risk potential.N-DBP is cytotoxic and genotoxic in lower concentration than regulated Carbonaceous-DBPs (C-DBPs).Free chlorine also give contribution of N-DBP formation because the reaction with ammonia in high concentration can produce of chloramines [6].In order that, increase of N-DBPs precursors also affect by the presence of algae and wastewater in the surface water both of them are dissolved organic nitrogen sources [8].It found at cell mammalian test that N-DBPs groups such as haloacetonitriles (HANs), halonitromethanes (HNMs) and haloacetamides have level of cytotoxic and genotoxic higher than the THMs and HAAs, although the haloacetaldehydes show the toxicity in high level too [10].
Currently, the investigation of DBPs' formation from different types of water sources is very important.The health risk potential must be concern to remove the DBPs from drinking water.DBPs is very harmful for human beings because of carcinogenicity, cytotoxicity, teratogenicity and mutagenicity [11].The mechanism of DBPs formation and the health risk potential of Trihalomethane and Nitrosodmethylamin explicitly discussed so that it can be understood that DBP formation can be prevented.This study aims to analyze all possible health risks caused by DBPs formation in drinking water, the risks to human health as the most active consumption of drinking water.From this analysis, the best strategy can be determined to prevent or reduce the formation of DBPs through process modification or the addition of advanced technology.

Methodology
The critical review focused on the analysis of DBPs potential formation, diagnosis how the organic matter affects the formation of DBPs.Find the most DBPs in drinking water such as THM as Carbonaceous DBPs and also Nitrosamine as Nitrogenous DBPs that indicated the wastewater pollution.
In order to conduct this study, the analysis refers to international journal with database from Google Scholar, PubMed, Scopus, Science Direct, and other water journal by searching the main keyword disinfection process, disinfection by products, health impact of DBPs and removal technologies for DBPs.Research articles and journal was restricted in the field of water treatment especially disinfection process.
The framework of this paper begins with an analysis of pollutant sources as precursors of the DBPs formation, the factors that affect the DBPs formation and the importance of advanced treatment in reducing toxicity levels are shown in Figure 1.

Formation of DBPs
The DBPs is formed by the reaction between organic matter and chlorine in water.The natural organic matter (NOM), are generated from fulvic, anthropogenic origin and humic acids with the average concentration in water in the range of 2-10 ppm.Both DOM and NOM play role as precursor that react with disinfection agents form the DBPs.They are had potential human health risk [12,13].Characteristic and quality of source water affect the DBPs formation including type and amount concentration of organic matter, temperature of the environment, pH, disinfection agent and dosage, and reaction time during the disinfection process [14].The presence of recalcitrant micropollutants, has an influence on the diversity of DBPs as organic intermediate and/or products of disinfection process [15].Micropollutants and the intermediate transformation and/or products play role as the precursor DBPs when the UV/chlorination of disinfection process [15].
The formation of DBPs was found in many types of disinfection process, such as chlorination, chloramines, and also ozonation.Table 1 explains the structure of DBPs and alternative disinfection that will form the DBPs, respectively.
The important species of N-DBPs are haloacetonitriles (HANs), haloacetamides (HAcAms), Nitrosamine (NAs), cyanogen halides (CNX), halonitromethanes (HNMs), N-nitrosomethylethylamine (NMEA): Cyanogen chloride (CNCl), cyanogen bromide (CNBr), Trichloronitromethane (chloropicrin), tribromonitromethane (bromopicrin), bromodichloronitromethane, dibromochloronitromethane, N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), Nnitrosomorpholine (NMOR), N-nitrosodiethylamine (NDEA) [8].When investigating the presence of THMs, there are four compounds always be mention (see Figure 2).They are always stay in liquid at room temperature, poorly soluble and tend to volatile in water [13].The time of reaction between organic matter and disinfection agent affect the production of DBPs.The formation of THMs, HAAs and HNMs are getting higher as the chlorination reaction time and decrease after 2 hours of reaction time.The reaction time that produces the most DBPs at 20 hours and 70 hours of chlorination reaction.Disinfection process from chlorination and chloramination also affect by dose of disinfection agent so that DBPs formation increase together with the increase dose.The DBPs formation of chlorination increase almost 5 times higher that chloramine disinfection that only 1.5 times increase.

DBPs Health Risk Potential
Since 1970, the disinfection process has the potential to endanger human health due to reactions that occur between organic compounds in water and disinfection agents, it always be the big reason of many researchers.However, the drinking water process can't leave the disinfection because of the role of inactivation the pathogenic microorganisms [13].The unexpected formation of DBPs in drinking water and wastewater treatment can cause important problems for human health and environmental safety because the DBPs have been found the potential of cytotoxicity, genotoxicity, and lead to toxicity [15].

Human Health Risk Potential
Many DBPs have been identified as carcinogenic compounds and potentially risk human health.DBPs is volatile compounds, found as potentially risk human health because they have potential of carcinogenic and mutagenic [13].Epidemiologists make a correlation of THM exposure through various types of contact routes with the risk of various types of cancer, especially in the digestive (bowel) and excretory (bladder) systems.Based on that, the USEPA dan WHO together with the European Union assign the regulations on the limits of DBPs concentration in the water that can be consumed by humans.For total trihalomethane in water, USA set up the limit is 80 µg L−1 in, for Germany 50 µg L−1, and Canada, Brazil and European Union together set up the limit on 100 µg L− 1 [15].1239 (2023) 012027 IOP Publishing doi:10.1088/1755-1315/1239/1/0120276 DBPs exposure the human health in three ways: ingestion, dermal absorption and inhalation [13,16].For THM, the most exposure pathway is oral ingestion to human beings.Via dermal pathway, the skin contact is the most possible from washing activities and showering.Both of dermal and inhalation still have significant report of risk potential.Chloroform has higher risk potential than other TMHs so that when it found in water treatment it may led high health risk effect [16].Exposure to THM has also been specifically reported in disorders that cause pregnancy problems such as miscarriage, stillbirth, premature birth, intrauterine growth retardation, umbilical cord entanglement, placental problems, fetal hypoxia/asphyxia, and several other pregnancy problems [17].
Likewise, N-DBPs such as haloacetonitriles and halonitromethanes are an important concern because they have significantly higher potential for genotoxicity and cytotoxicity than C-DBPs.The presence of amine groups in water as kind of organic compounds (atenolol, ranitidine, and ethanolamine) play the important role as N-DBPs precursors [17].N-DBPs generally come in a lower concentration than C-DBPs but potentially give the higher health risk.In vitro mammalian cell assays have found that some type of N-DBPs have the higher levels of cytotoxicity and genotoxicity than THMs and HAAs.The application of disinfection in reclaiming wastewater for various activities is being done in many countries to prevent the potential of waterborne diseases.However, the presence of dissolved organic matter (DOM) in wastewater effluent significantly enriched the nitrogen in water (i.e., to be precursors of N-DBPs) than organics natural matter from surface waters [17].Several types of N-DBPs are grouped internationally as compounds with a high potential risk of developing cancer if daily consumption exceeds safe limits [18].Of the various types of N-DBPs, it was found that NDMA is the DBPs compound with the greatest potential for cancer risk even though its concentration is present in very small amounts [2].
Review of the occurrence, carcinogenic potential, and genotoxic potential have been done in many studies more than 30 years since DBPs found in drinking water at 1974 by Rook and others.The listed of Table 2 about the summary occurrence, carcinogenicity and genotoxicity of regulated DBPs (THMs and HAAs) and also for unregulated DBPs (Nitrosamines) [19]  The presence of DBPs in drinking water is an important concern for human health because it causes serious problems due to continuous exposure and the ability of DBPs to increase the risk of developing cancer in the human body, disorders of the liver, kidneys and the nervous system and reproductive system [20].The variety of DBPs that exist today is influenced by how DBPs were formed, so the diversity and complexity of their impacts on the environment and humans need to be studied properly.Because the characteristic of some types of DBP indicates that the compound is persistent, difficult to degrade biologically and is found in low concentrations, DBP is often considered as an emerging pollutant that can have more harmful effects than other contaminants [21].
Seeing the potential impact on human health, it is necessary to think about the ways to prevent and reduce the potential formation of DBPs in water treatment which requires disinfection process.Investigate the presence of organic precursors in water and determining the correct chlorine dosage can help prevent the formation of DBPs in water, especially drinking water.Additional technology in water treatment may be required as an effort to reduce the presence of precursors before the disinfection process and add further treatment to remove DBPs that are formed before the water is distributed.

Conclusions
Disinfection process is effective to inactivation pathogen microorganism in water and wastewater treatment.However, chlorine, chloramine and ozone disinfection process have potential formation the disinfection byproducts (DBPs).The most DBPs of water treatment is Trihalomethanes groups and for wastewater treatment the Nitrogenous DBPs is the most DBPs formation.DBPs have the potential of cytotoxicity, genotoxicity, and lead to toxicity

Figure 2 .
Figure 2. Most common type of trihalomethane in drinking water[13]