methylation into methyltriclosan [MTCS

methylation into methyltriclosan MTCS; 5-chloro-2-(2, 4 dichloropheoxy) anisole (Boehmer et al., 2004; Bester, 2005), which is more lipophilic in nature, which is then released into receiving environment. Nuria et al. (2013) identified the presence of Methyltriclosan in fish which has been used as a marker of exposure to WWTP effluent. Hence, the lipophilicity of Methyltriclosan and its resistance to biodegradation and photolysis processes makes the mobilite to exhibit a higher degree of environmental persistence than its parent compound (Lindstrom et al., 2002). A large fraction of TCS loss is transformed to Methyl-TCS. Majority of TCS recovered as Methyl-TCS about 16.5 and 50.6 % respectively. For Methyl-TCS, the MDL was found to be 0.25 and 1.4 ng g-1 wet wt and for biosolids was about 0.48 and 26.6 ng g-1 respectively. Also, the half-life of TCS was determined as 104 days and the Methyl-TCS was more persistent than TCS and was estimated to be as 443 days. Balmer et al. (2004) have explained about the formation of Methyl-TCS through biological methylation in different WWTP process obviously limits the total TCS removal because the transformation products of TCS is much more resistant to photolysis. Lindstrom et al. (2002) said in aqueous region, TCS is readily degraded in the environment with relative increase of Methyl-TCS increases in summer, and nearly equal to the residual TCS concentration in the upper region of surface water. He also explained the slow reversion to the parent compound in fish liver and intestine, Methyl-TCS will bioaccumulate upon chronic exposure and posing a potential threat to humans as a result of fish consumption (James et al. 2012).
Methyl-TCS is typically found in much lower concentrations than those of TCS with ratios (Methyl-TCS/TCS) between 0.01 and 0.05 for effluent, surface water, sludge, and sediment (Bester, 2005). McAvoy et al. (2002) have documented that the Methyl-TCS/TCS ratio can largely exceed in effluent, surface water, sludge, and sediment. Benny et al. (2014) showed that the Methyl-TCS fraction can become substantially higher in environment where TCS is readily degraded relative to Methyl-TCS (such as at the air?liquid interface of lakes) as well as in high microbial activity (such as aerobic composters). This transformation of TCS into Methyl-TCS will ultimately increase the environmental persistency of triclosan, because the methylation increases the bioaccumulation potential and limits the biodegradation of total TCS congeners (i.e., the sum of Methyl-TCS and TCS).
2.8.2. Dioxins
There has been increasing concern regarding the degradation and the transformation of TCS during manufacturing, incineration and in the aquatic environment which leads to dioxin toxicity. The photolysis is the major pathway of the antimicrobial in the aquatic environment, which documented the formation of 2,8-dichlorodibenzodioxin (DCDD) and other dioxin derivatives during the photo degradation of TCS in aqueous solutions (Aranami and Readman, 2007). The pH of aqueous solutions spiked with TCS influences the formation of dioxin by-products and Latch et al. (2003) reported that 1–12% of TCS is converted to DCDD in aqueous solutions buffered at a pH 8 or above and concluded that, in sunlight-irradiated waters, the conversion of TCS into dioxin by-products is dependent on both the pH and irradiation wavelength.
Mezcua et al. (2004) investigated the photo degradation of TCS to dioxins in wastewater samples and the study indicated that 2, 7/2, 8-dibenzodichloro-p-dioxin is a by-product of the TCS, with 8 ?g ml-1 of antimicrobial were spiked in both water and wastewater samples. These results were consistent with phototransformation of triclosan and the degree of photolytic conversion was dependent upon pH and the organic matter content in the sample. Sanchez-Prado et al. (2006) were the first to use a solar simulator photoreactor, in combination with actual contaminated wastewater samples, identified the formation of 2, 8-DCDD and a possible DCDD isomer or dichlorohydroxydibenzofuran independently in the sample. The photochemical reaction of triclosan accounts 80% loss of epilimnion region of Lake Greifensee during summer season.
Aranami and Readman (2007) irradiated the freshwater and seawater samples with a low-intensity using artificial white light source for a 12 day period. The photodegradation of TCS produced DCDD, in the 3rd day of irradiation that occured in both freshwater and seawater samples, after 3 days of irradiation. The photochemical conversion of TCS in natural water samples of Mississippi River and Lake Josephine waters was investigated by Buth et al. (2009). This conversion of chlorinated triclosan derivatives into dioxins was substantiated in natural and buffered pure water, with yields of 0.5–2.5%, respectively. The majority of TCS is photolytically transformation products, along with the environmental factors influencing their degradation (Aranami and Readman, 2007) and quantifying the level of risk to both aquatic environments and humans is determining to what extent and under which environmental conditions the conversion of TCS into toxic by-products occurs.
2.8.3. Chlorophenols
The photochemical transformation of TCS also produce 2, 4-dichlorophenol and 2, 4, 6-trichlorophenol, which the US EPA has pointed as priority pollutants. The formation of chlorophenols from TCS was demonstrated by Kanetoshi et al. (1987) however; the higher concentrations of chlorine and TCS are relevant to environment. Later (Greyshock and Vikesland, 2006) validated that chlorophenols are transformation products of TCS, in the low levels of chlorine or chloramines. TCS reacted with free chlorine under drinking water conditions and 2,4-dichlorophenol was formed through the ether cleavage of TCS, which then undergoes electrophilic substitution to form 2,4,6-trichlorophenol.
The effect of pH on the formation of TCS byproducts were demonstrated by Rule et al. (2005) that it was primarily ionized the phenolate form of TCS that reacts with hypochloric acid. Canosa et al. (2005) tested at low concentrations of TCS (ng mL?1) and chlorine (mg L?1) with this test, 2, 4-dichlorophenol and 2, 4, 6-trichlorophenol were detected in all of the samples. Even though, the molar yields of TCS conversion were less than 10% and it has demonstrated that these two phenolic by-products are relatively stable over time and potentially toxic Fiss et al. (2007).
2.8.4 Chloroform
The presence of TCS in various consumer products will react with free chlorine or chloramine to produce chloroform and other chlorinated triclosan products with different pH by Greyshock and Vikesland (2006). Fiss et al. (2007) also assessed the propensity of a dish soap containing TCS to form chloroform when added to chlorinated water and assessed after 5 min and 120 min, the concentration of chloroform was produced from 15 to 50 ?g l?1. and the significant amounts of chloroform may be formed during the daily use of household products containing the antimicrobial properties. The conversion of TCS to chlorinated derivatives is also dependent on temperature, chloroform yields higher in increased temperatures. An exposure model completed by Fiss et al. (2007) indicated that, under certain conditions, the amount of chloroform produced could be significant, which may place consumers at an increased risk for adverse health effects.
2.9. Effects of Triclosan on aquatic organisms
Triclosan is a ubiquitous because of continuous discharge of chemicals into waste water streams. Hence, the incomplete removal of Triclosan results in contamination of water, soil and other organisms. Orvos et al. (2002) reported on most drugs that targets humans, in which exhibits higher toxicity to many lower trophic organisms, such as microalgae. Wilson et al. (2003) reported the significant changes in phytoplankton community that exposed to TCS concentration as low as 15 ng L-1 and approximately 33% reduction in algal genus richness at 150 ng L-1.
Hence, the peak levels of 3800 and 5160 ng L-1 at two sites of Tamiraparani River indicate the high risk on algal communities. Buser et al. (2006) reported the higher concentrations of Methyl-TCS were found in fish as high as 2100 ng g-1 (Veldhoen et al. 2006). Veldhoen et al. (2006) reported the effects of TCS on thyroxin-induced metamorphosis in frog tadpoles and some algae at a concentration ranges from 100 – 150 ng L-1.
2.9.1. Algae and invertebrates
Algae were determined to be the most susceptible organisms. It is primary food source for many aquatic species, constitute a specific pathway for the accumulation of lipophilic water-borne contaminants, such as TCS (Capdevielle et al., 2008). Due to continual exposure of TCS, leads to incomplete removal during the wastewater treatment process in receiving waters, and increasing their accumulation of the antimicrobial properties and its degradation products in the tissues of aquatic organisms. From these measurements, bioaccumulation factors of 1100 and 1600 ?g kg?1 were estimated for parent compound and its methylated by-product. Coogan et al. (2007) sampled the filamentous algae (Cladophora spp.) in a receiving stream from the city of Denton (Texas) for measuring of TCS and MTCS and were ranged between 100–150 and 50–89 ?g kg?1, respectively. Also, the bioaccumulation potential of TCS and MTCS was also determined in freshwater snails (Helisoma trivolvis) and in algae (Cladophora spp.), using GC-MS (Coogan and La Point, 2008). Bioaccumulation concentrations of TCS and MTCS for snail tissue were 500 and 1200 ?g kg?1, respectively. The algal bioaccumulation of TCS were also high, 1400 and 1200 ?g kg?1, respectively. Tatarazako et al. (2004) showed the result the microalgae (0.15 mg L-1) are very sensitive to triclosan than bacteria and fish. In a study by DeLorenzo et al. (2008), adult grass shrimp (Palaemonetes pugio) were exposed to 100 ?g l?1 of TCS and they were found to accumulate as MTCS after a 14-day exposure period. This finding provides evidence for both the conversion of TCS to MTCS in seawater, and their bioaccumulation potential. Though MTCS is resistant to the processes of biodegradation and has the ability to persist in the environment for longer periods of time than the parent compound. Many aquatic invertebrates depend on algae as a source of nutrients, by which it leads increase of TCS concentration in many aquatic organisms.
2.9.2. Fish
Miyazaki et al. (1984) was the first to report the presence of MTCS in aquatic biota. In fish, TCS and its byproducts have been detected in higher level of concentration. From Tama River and Tokyo Bay, fish and shellfish were collected, then TCS and MTCS was identified by GC-MS in all the fish samples (1–38 ?g kg?1 whole body) and shellfish samples (3–20 ?g kg?1). A study by Adolfsson-Erici et al. (2002) who measured TCS levels in rainbow trout (Oncorhynchus mykiss) in the waters of a WWTP in Sweden. Bile fluid of fish contained TCS at concentrations ranging from