Pharmaceutical and personal care products (PPCPs) like cosmetics, soaps, disinfectants and detergents are composed of a plethora of chemical classes including antimicrobial compounds. Triclocarban (TCC) is a popularly incorporated antimicrobial since it prevents product spoilage and infection to the consumer.
The Journey of TCC
PPCPs are consumed globally at a rate of 0.1 million tonnes per year and find their way into waste water treatment plants [1].
76-79% of triclocarban (TCC) is released with sewage sludge since it is difficult
to degrade using existing, implemented methods [2].
TCC is omnipresent and preserved in the environment and even found to accumulate within our flora and fauna,
causing hormone disruption and aiding anti-bacterial resistance.
Extent of TCC Accumulation
At local wastewater treatment plants (WWTPs) in Udupi and Mangalore, India, the average
concentration of TCC recorded in the sludge was 21,000 ng/g dw and 13,000 ng/g dw,
respectively [3].
The concentration of TCC detected in Indian aquatic environments (including surface waters or even drinking
water) was 1119 ng/L [2].
On a global scale, the median values of detected TCC in surface water worldwide ranged around 10-100 ng/L. 51-347
ng/L and 7.5-102 ng/L TCC were monitored in tap and treated drinking water, respectively [4].
Damage to Aquatics
Pertaining to Indian waters, 692 ng/g w/w TCC was accumulated in fish from the Kaveri
River, India [5]. Victims and their symptoms included:
Zebrafish larvae: Affected nervous system & skeletal muscle development, metabolism along with hormonal
conditions.
Fathead minnows: Reduced mobility & feeding, aggression, fecundity and even death.
Freshwater mud snails, planktonic crustaceans, and amphibians: Reproductive issues rooted from
endocrine-disruption.
Damage to Agro Industry
In food crops cultured in contaminated hydroponic media, after four weeks of
exposure, roots accumulated 86–1,350 mg kg−1 of antimicrobials and shoots had accumulated 0.33-5.35 mg kg−1 of
antimicrobials, including triclocarban [6].
The uptake and accumulation of TCC due to the use of contaminated biosolids as fertilisers has been
detected in several food crops—carrots, green peppers, tomatoes, and cucumbers—and has been proven to hinder
proper metabolism in the crops [2].
Accumulation of TCC was observed in soil and soil-dwelling organisms. Moreover, microbial communities and their
metabolic activities like nitrification and denitrification were heavily affected. As an antimicrobial, it may
participate in antibiotic resistance bacteria selection and may induce antibiotic-resistant genes in these
bacteria [2].
Existing Methods
Adsorption is the most prevalent physical approach to removing TCC from water, but there
is room for improvement in its operational parameters. Additionally, desorption should be considered to ensure
sustainable water treatment. Although activated carbon adsorption has been considered, its disadvantages include
high costs, lack of selectivity, and a limited regenerative capacity [7].
In the case of chemical methods, Ultraviolet light (UV), chlorine oxidation, ozone, and electron-Fenton are
usually considered promising methods. Inorganic ions, like sulphate and nitrate, often found in wastewater, were
found to hinder the photolysis of TCC by UV radiation [8]. Chlorine oxidation often results in the
incomplete degradation of the compounds and the production of hazardous byproducts. Chemical approaches are
generally more expensive, while ozone-based techniques have been proven to be less effective.
It was found that most methods currently utilised by WWTPs in India aren’t adequate for removing TCC [2].
Biodegradation of TCC
Isolated from a WWTP in China, Ochrobactrum sp. TCC-2 expresses an amidase enzyme through the TccA gene which can break down TCC. However, according to literature, it was found to degrade TCC to toxic byproducts 3,4-Dichloroaniline (3,4-DCA) and 4-Chloroaniline (4-CA). Amidase also showed activity with amide bond cleavage in carbanilide, dichlorocarbanilide, trichlorocarbanilide.
Chloroanilines
Once degraded by existing methods, toxic chloroaniline byproducts accumulate in the environment. According to studies conducted by the World Health Organisation and Centers for Disease Control and Prevention, 4-chloroaniline and 3,4-dichloroaniline act as carcinogens and cause methemoglobinemia-which is a condition characterised by an abnormal form of haemoglobin in the blood leading to cyanosis and hypoxia.
Our Solution
- Some bacteria, through other degradation pathways, can degrade the initial byproducts 3,4-DCA and 4-CA to Krebs’ cycle intermediates which are then utilised by the bacteria.
- Our proposed solution to degrade TCC into non-toxic final products was to insert the novel amidase gene into a chassis which degrades its byproducts.
- Our project involves modifying a known metabolic pathway by adding one step to it.
- Our novel amidase gene acts along with a cluster of native genes that degrade the compound till cis,cis-muconic acid which is then further taken into the Krebs' cycle.
- Recognizing that our project involves genetically modified components that can have unintended consequences, especially when released into the environment, we have modified a kill switch such that it can provide a gene knockout strategy through a CRISPR-Cas9 system in the presence of blue light. This will serve as one of the biocontainment strategies. To know more, click here.
References
[1] Gopal, C. M., Bhat, K., Ramaswamy, B. R., Kumar, V., Singhal, R. K., Basu, H.,
Udayashankar, H. N., Vasantharaju, S. G., Praveenkumarreddy, Y., Lino, Y., & Balakrishna, K. (2021). Seasonal
occurrence and risk assessment of pharmaceutical and personal care products in Bengaluru rivers and lakes, India.
Journal of Environmental Chemical Engineering, 9(4), 105610. https://doi.org/10.1016/j.jece.2021.105610
[2] Yun, H., Liang, B., Kong, D., Li, X., & Wang, A. (2020). Fate, risk and removal of triclocarban: A critical
review. Journal of Hazardous Materials, 387, 121944. https://doi.org/10.1016/j.jhazmat.2019.121944
[3] Subedi, B., Balakrishna, K., Joshua, D. I., & Kannan, K. (2017). Mass loading and removal of pharmaceuticals
and personal care products including psychoactives, antihypertensives, and antibiotics in two sewage treatment
plants in southern India. Chemosphere, 167, 429-437. https://doi.org/10.1016/j.chemosphere.2016.10.026
[4] Shen, J. Y., Chang, M. S., Yang, H., & Wu, G. J. (2012). Simultaneous determination of triclosan,
triclocarban, and transformation products of triclocarban in aqueous samples using solid-phase
micro-extraction-HPLC-MS/MS. Journal of Separation Science, 35(19), 2544-2552. https://doi.org/10.1002/jssc.201200181
[5] Vimalkumar, K., Seethappan, S., & Pugazhendhi, A. (2019). Fate of Triclocarban (TCC) in aquatic and
terrestrial systems and human exposure. Chemosphere, 230, 201-209.
https://doi.org/10.1016/j.chemosphere.2019.04.145
[6] Mathews, S., Henderson, S. & Reinhold, D. Uptake and accumulation of antimicrobials, triclocarban and
triclosan, by food crops in a hydroponic system. Environ Sci Pollut Res 21, 6025–6033 (2014). https://doi.org/10.1007/s11356-013-2474-3
[7] Grégorio Crini, Eric Lichtfouse. Advantages and disadvantages of techniques used for wastewater treatment.
Environmental Chemistry Letters, 2019, 17 (1), pp.145-155. https://doi.org/10.1007/s10311-018-0785-9
[8] Azeezah Amigun Taiwo, Saheed Mustapha, Tijani Jimoh Oladejo, Adekola Folahan Amoo & Rabi Elabor (2022):
Occurrence, effects, detection, and photodegradation of triclosan and triclocarban in the environment: a review,
International Journal of Environmental Analytical Chemistry, https://doi.org/10.1080/03067319.2022.2106860
[9] Ebele, A. J., Abdallah, M. A., & Harrad, S. (2017). Pharmaceuticals and personal care products (PPCPs) in
the freshwater aquatic environment. Emerging Contaminants, 3(1), 1-16. https://doi.org/10.1016/j.emcon.2016.12.004