Do you ever stop and reflect on the small choices you make in your everyday life and what consequences it might have on your surroundings? Many of the chores and tasks we do daily may contribute significantly to the ever growing microplastic littering in marine habitats. In fact, a single basket of laundry may release as much as 700 000 microplastic particles with each wash [1]. Meanwhile, practicing sports on an artificial grass field contributes to the cumulative release of several tons of microplastic debris every year [2]. Indeed, making a conscious effort in your daily life will have a direct impact on the future of Earth.

Microplastics are tiny fragments of plastics, less than five millimeters long, that tend to accumulate in the environment due to low degradability [3]. The origin of these fragments can be divided into two larger categories; primary and secondary sources [4]. Primary sources correspond to personal care products and deterioration of larger plastic objects. Examples include shower gels, wear of car tyres and synthetic textiles [5]. Secondary sources originate from slower mechanical or chemical weathering processes on plastics already disposed in nature, as observed in long-term UV degradation of larger plastic bodies [3].

While there exists only limited evidence supporting the toxicity of direct exposure to microplastics, such as shedding from fleece clothing, the potential risk to biota and humans increases drastically when the fragments reach larger bodies of water [6]. To the primary consumers, the small plastic pieces can look indistinguishable from food stuff, allowing microplastics to enter the food chain. The particles have shown a propensity of accumulating upwards and are known to cause blockage of the gastrointestinal tract and interference with the reproduction of higher organisms [7]. Another concern of water-bound microplastics lies in their affinity for hydrophobic compounds. Both heavy metals and persistent organic pollutants, two priority pollutants according to the EPA Clean Water Act, end up accumulating around them [6][8]. Since these compounds often have high bioavailability and are only bound to the plastic through weak association, they readily leach off the plastic and can cause adverse effects on the endocrine system and central nervous system [9] [10]. Similarly, plasticizers, or low-weight phthalates, which are common additives in commercial plastics that offer improved flexibility and ductility, have been known to cause hormonal disruption in humans and wildlife [11].

Surely, with extensive research corroborating the complications of microplastics, stringent laws and regulations ought to have been put in place to prohibit microplastic pollution - to protect the marine biodiversity and human health?

Well, not quite.

According to the United Nations Environment Programme, microplastics started to appear in in consumable goods about fifty years ago and up until a few years ago the consumer awareness of their potential ramifications was close to nonexistent. However, in the past few years, the consumer apathy with regards to the subject started to cease and political actions were finally put in place. In 2015, former President Obama signed the Microbead-Free Waters Act of 2015, consequently banning plastic additives in cosmetics and personal care products in the US [12] [13]. Some countries have since then followed suit, but far from the majority. Perhaps most notably, the European Union has not made any considerable strides toward the banning of microplastic products [11].

Recent discussions regarding the realization of the UN development goal number 14 [14] concerning the conservation and sustainable use of marine resources once again shed light on the matter and triggered a demand from consumers that retailers limit the amount of products containing microplastics. This caused a domino-effect in the entire supply chain that forced businesses to act to prevent them from losing their competitive edge on the market. Consequently, several retailers with significant market shares chose to stop handing out free plastic bags and selling personal care products containing microplastics [15] [16].

While the issue is being addressed and regulations are moving in the right direction, the process is slow and without a realistic end in sight. We, team iGEM Lund, have therefore chosen to devote this year to participate in the world-wide engagement against microplastic accumulation in the ocean, in line with the United Nations new framework for sustainable development.

How can synthetic biology aid?

With some clever insight into the dynamics of synthetic biology, it can be harnessed to combat various aspect of marine debris. This has been recognized by previous iGEM teams throughout the years and the problem of microplastics in particular has been targeted multiple times, mainly through different methods of biotic degradation [17] [18] [19]. However, while bio-degradation would certainly be the preferred approach, as it eliminates the plastic once and for all, the process is very time-consuming and it does not compete with the abiotic degradation methods that exists today [20] [21]. With this in mind, we set out to apply our knowledge of synthetic biology to alleviate the current microplastic situation.

After dialogues with water sanitation experts, it was made apparent that not only does the Swedish government allocate very little resources to the sanitation of microplastics in water treatment plants, but that there exists no quick and easy way of even detecting whether sanitation might be necessary without the use of expensive laboratory equipment and arduous filtration processes. Currently, the most efficient method of assessing microplastic content is through sieving and several subsequent filtration and separation steps [22]. A simple tool to evaluate the presence of microplastics would therefore be very helpful in that regard. Consequently, μSense was born.

Our solution

For this year’s iGEM competition, we have decided to engineer a simple, novel biosensor with the goal of determining the presence of microplastics in freshwater. The sensor will be realized by design and implementation of a genetic circuit into Escherichia coli. A logic AND-gate will be constructed using the expression of two heterologous sensory elements to detect the presence of microplastics. For more information, see project design.


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