Contents

• 1) Introduction
• 2) The Problem
  • 2.1) Heavy Metal Pollution
  • 2.2) Plastic Pollution
• 3) Current Solutions
  • 3.1) Heavy Metal Pollution
  • 3.2) Plastic Pollution
• 4) Our Solution
  • 4.1) Heavy Metal Biosensor
  • 4.2) Bioremediation
  • 4.2) PET Plastic Biodegradation
• References

Introduction

Our vision is to devise a system enabling access to clean and potable water for Ghana and beyond. Our project aims to detect and remove the two major water contaminants in Ghana’s water: heavy metals and plastics by employing cell-free systems that implement synthetic biology to sustainably remove these contaminants. To this extent, we designed PETALUTION; a holistic approach to water health based on cell-free synthetic biology, where heavy metal biosensors, a heavy metal sequestering bioremediation device through metallothionein-mediated binding, and an enzyme cocktail for polyethylene terephthalate (PET biodegradation. We believe that PETALUTION can be expanded as a platform to target more water pollutants which could offer cell-free biological solutions to water pollution around the world. On this page, we discuss the problem we are trying to solve, the current solutions and our solution.

The Problem

Water quality is of growing concern in Ghana with about 60% of the water bodies being polluted and most are in critical condition (1). The main cause of this pollution is unregulated industrial activities such as illegal mining and poor plastic waste management. River bodies in Ghana that have for many years served as a source of water for residents, have now been polluted as a result of these unregulated and illegal activities.

Heavy Metal Pollution

Ghana is the leading producer of gold in Africa, with about 35% of gold being extracted by small-scale miners, most of them operating illegally (2). Because of the high amount of water required to wash the gold, illegal miners frequently work by nearby water bodies. They will then discharge contaminated materials from the gold mining (tailings) directly into the nearby water bodies. The common waste products from this process are mercury, arsenic, copper and lead (3). These processes can cause severe environmental damage to the water bodies. Notable among them are River Pra, Daboase, and River Birim in Ghana. These rivers and their tributaries have been reported to contain levels of heavy metals such as cadmium, mercury and lead much higher than the maximum accepted concentrations established by the World Health Organisation (WHO). In the Birim river, they have found water samples which have shown lead, mercury, and cadmium levels 400, 180, and 15 times over the WHO limit, respectively (4).

Heavy metal pollution also poses a serious public health risk, threatening the health of communities dependent on these water bodies. Ingestion of heavy metal-contaminated water can lead to kidney damage and neurotoxic effects (mainly affecting children) (3). There is also a growing concern about heavy metal accumulation in soil and crops since most of these illegal mining sites are located near farmlands. An assessment of heavy metal contamination in surface soils and plants on the West Coast of Ghana revealed that lead was observed in the highest concentrations in plant samples, exceeding by over 17-fold, the Food and Agricultural Organization (FAO) permissible limit of 5mg/kg. Cadmium (17.47 mg/kg) was also detected in plants at levels that surpassed the 0.20mg/kg limit set by the FAO. Given the prevalence of these metals at alarming concentrations, this is a significant threat to plant productivity, thus a threat to food security and public health (5). This also poses a risk to the Ghanaian economy since the country may no longer be able to sell this produce outside Ghana.

Plastic Pollution

Ghana generates over 3000 tonnes of plastic waste daily with an estimated 250,000 tonnes dumped into the Atlantic Ocean annually (6). Much waste won’t be properly recycled as many places within the country lack the infrastructure to properly deal with the plastic. The plastic which is not recycled will either end up in landfills or will accumulate in the environment and end up in the ocean.

The plastic waste left in the environment contributes to the contamination of groundwater and has caused adverse effects on the local wildlife. They found that microplastics (created from the excess plastic waste in the water and environment) were a significant burden to aquatic life as the frequency of occurrence of microplastics in three fish species in the Gulf of Guinea (among one of the most densely marine litter polluted regions in Ghana) was alarmingly high: Sardinella maderensis (41%), Dentex angolensis (33%), and Sardinella aurita (26%) (6). This pollution not only causes a direct impact on the aquatic life in Ghana’s water but has also compromised fish as a local food source. In addition to the effect on wildlife undisposed plastic can build up in drains and cause flooding. An example of this would be the Asylum Down gutter in Ghana, which occasionally gets blocked, leading to stagnant water – a breeding ground for pathogens and disease-causing organisms (e.g. mosquitoes). Plastic-blocked waterways are resulting in poorer sanitation in these areas and is said to have been a significant factor in the worst cholera outbreak Ghana recorded back in 2014 (7).

More than 60% of Ghana’s municipal plastic content is made up of polyolefins (8), notable among them would be polyethylene terephthalate (PET) as not only does it takes many years to break down posing both physical and chemical threats to local ecosystems (9) it also lacks a low-energy degradation process meaning that Ghanaians will often have to burn the plastic to deal with the waste, which will contribute to air pollution.

Current solutions

Most of the main measures to control water pollution in Ghana involve government intervention by banning illegal mining sites leaching heavy metals into waterways and trying to create responsible waste management strategies and fiscal reforms by increasing the tax on importing plastic (10). Whilst much of this government intervention has been useful in lowering the rate of pollution, it may give a false sense of security as much of the water remains heavily polluted.

Solutions for Heavy Metal Pollution

There are currently very few methods to remediate heavy metals from the water without introducing large-scale water treatment infrastructures. Bioremediation techniques are currently seen as the solution to this problem; however, most existing bioremediation methods contain genetically modified organisms (11) (12) (13) and given the GMO restrictions across the world GMO-based bioremediation currently can’t offer a real-world solution.

Detection of the presence of heavy metals is extremely important in informing local authorities where the most acutely affected water is so they can inform the local communities if their water is too dangerous to consume or use for farming. Whilst there are relatively cheap methods to detect heavy metals in water such as Merck’s Spectroquant, a chemical-based colourimetric test, however, many of these tests don’t have the sensitivity to detect the WHO permissible concentration. For example, the cadmium cell test is only able to test between 0.025-1.000 mg/L but the guideline value from the WHO is 0.0003 mg/L. Most of these chemical tests including Spectroquant also require expensive propriety equipment which puts it out of reach of many individuals.

Solutions for Plastic Pollution

To deal with the current excess of plastic waste in Ghana the government have set up municipal waste companies like Zoomlion, which collect household plastic waste door to door and then recycle this plastic waste. PET plastic, however, cannot be sustainably processed by Zoomlion, so they must export the PET to other countries to deal with. For more information on how Zoomlion influenced PETALUTION, see the Human Practices tab.

Our solution

Before deciding our actual iGEM project, we knew we would be looking at water pollution as the Ghana side of our team wanted help with this issue. The Ghana side of the team suggested looking at plastic and heavy metals as tangible aspects of water pollution that could potentially be mitigated. Having narrowed down these two problems, given the nature of synthetic biology of looking to nature for examples in which biological systems deal with the environment, we identified PETases from Ideonella sakaiensis (14) and metallothioneins from Mytilus edulis (15), as potential targets of catalysing the mitigation of PET plastic and heavy metal pollution, respectively.

We looked at previous iGEM teams for inspiration on how we could use these target proteins to tackle these problems. We looked at the Edinburgh 2020 Overgraduate project (Nemo) and the 2021 project (Supergrinder) as well as ASU’s 2021 project (Chalmydomon [As]) which all helped us produce the biosensor, PET biodegration and heavy metal bioremdiation parts of our project.

Having this in mind, our overarching goal was to establish PETALUTION, a holistic approach to water pollution, where PET plastic and heavy metals can be safely processed as contributing pollutants that are preventing local communities from being able to safely use potable water from the rivers (Figure 2). More importantly, we wanted to ensure a biosafe approach, delivering all aspects of PETALUTION as cell-free devices thus addressing any GMO-related socio-political issues.

Heavy Metal Biosensor

For the heavy metal biosensor, we designed a transcription-only cell-free biosensor, that in the presence of cadmium, lead, arsenic or mercury will cause fluorescence by transcribing an RNA aptamer which can then bind to a fluorophore which induces fluorescence. Making a cell-free biosensor also reduces potential risks to the environment and making it transcription-only minimises the device’s necessary components effectively increasing usability as compared to a cell-based biosensor.

Bioremediation

For heavy metal bioremediation, metallothioneins – metal-chelating proteins obtained from a variety of aquatic species including Mytilus edulis and Callinectes sapidus, formed the basis of the bioremediation device. Cell lysate from recombinant metallothionein-producing E. coli will be immobilised in a cell-free bioremediation cellulose hydrogel. This will effectively sequester cadmium, lead, arsenic and mercury.

PET Plastic Biodegradation

We draw inspiration from the PETase activity first identified in Ideonella sakaiensis (14), where PET can be broken down and converted to monohydroxyethyl terephthalate (MHET) which can then be metabolised into terephthalic acid (TPA) and ethylene glycol (EG). Mutated varieties of the PETase enzyme were synthesised and then extracted from E. coli cell lysate. The PETase varieties were then immobilised on silica beads. These silica beads when placed in water can then successfully break down PET plastic in water.

For more information on the design of each tool please visit the design page.

References

1. Ampomah B. 60% of Ghana’s water bodies polluted. Water Resources Commission. 2017;.
2. Jan Pijpers R, van de Camp E, Fisher E, Massaro L, Calvimontes J, Lanzano C. Mining ‘Waste’: Repurposing Residues in Artisanal and Small-Scale Gold Mining. Ethnofoor. 2021;33(2, Waste):13-40.
3. Akpalu W, Normanyo A. Gold Mining Pollution and the Cost of Private Healthcare: The Case of Ghana. Ecological Economics. 2017;142:104-112.
4. Oppong Afum B. Heavy Metal Pollution in the Birim River of Ghana. International Journal of Environmental Monitoring and Analysis. 2016;4(3):65.
5. Fosu-Mensah B, Ofori A, Ofosuhene M, Ofori-Attah E, Nunoo F, Darko G. Assessment of Heavy Metal Contamination and Distribution in Surface Soils and Plants along the West Coast of Ghana. West African Journal of Applied Ecology. 2018;26.
6. Adika S, Mahu E, Crane R, Marchant R, Montford J, Folorunsho R et al. Microplastic ingestion by pelagic and demersal fish species from the Eastern Central Atlantic Ocean, off the Coast of Ghana. Marine Pollution Bulletin. 2020;153:110998.
7. Teta L, Chikokonya D, Madzoma M, Ruzvido M. Poor plastic waste management in Accra, Ghana. Map The System. 2022;.
8. Glaser J. New plastic recycling technology. Clean Technologies and Environmental Policy. 2017;19(3):627-636.
9. Adam I, Walker T, Clayton C, Carlos Bezerra J. Attitudinal and behavioural segments on single-use plastics in Ghana: Implications for reducing marine plastic pollution. Environmental Challenges. 2021;4:100185.
10. Mensah A. Tax elasticity of demand for plastic: the cause of plastic pollution in Ghana. Journal of Environmental Economics and Policy. 2020;10(1):28-42.
11. Bhattacharya A, Gupta A. Evaluation of Acinetobacter sp. B9 for Cr (VI) resistance and detoxification with potential application in bioremediation of heavy-metals-rich industrial wastewater. Environmental Science and Pollution Research. 2013;20(9):6628-6637.
12. Cheng X, Sheng L, Peng S, Thorley E, Cao H, Li K. Integrated mechanism of heavy metal bioremediation from soil to rice (Oryza sativa L.) mediated by Enterococcus faecium. Plant Growth Regulation. 2022;97(3):523-535.
13. Zhou Q, Chen Y, Yang M, Li W, Deng L. Enhanced bioremediation of heavy metal from effluent by sulfate-reducing bacteria with copper–iron bimetallic particles support. Bioresource Technology. 2013;136:413-417.
14. Yoshida S, Hiraga K, Taniguchi I, Oda K. Ideonella sakaiensis, PETase, and MHETase: From identification of microbial PET degradation to enzyme characterization. Methods in Enzymology. 2021;:187-205.
15. Leignel V, Laulier M. Isolation and characterization of Mytilus edulis metallothionein genes. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology. 2006;142(1-2):12-18.