human-practices
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Description

Table of contents

Overview Impact of microplastics in the environment Motivation Our solution

Overview

Over the past decades, the widespread use of plastics has led to one of the most urgent and complex environmental challenges of our time. Plastics are revolutionary materials because of their versatility, lightness and strength. In fact, they are used in many common objects such as bottles, food containers, clothes, cosmetics and also tires. The main concern is the billions of plastics produced that are difficult to recycle and consequently accumulate in oceans, lakes, and the environment. Furthermore, due to weathering, light, and abrasion, plastics have the tendency to fragment into particles smaller than 5mm in size, called microplastics.

Impact of microplastics in the environment

Nowadays, microplastics are contaminating our oceans, rivers, and lakes, and harming aquatic life. They are often mistaken for food by fishes and other aquatic species, leading to ingestion and even death, thus entering the food chain and endangering human health.4 Studies have shown that the presence of high levels of microplastics in the blood can cause problems with the nervous system, disrupt metabolism, lead to obesity and thyroid disorders, trigger diabetes and infertility and, in severe cases, can lead to cancer.1 Another major concern is that microplastics can act as carriers of toxic chemicals, further increasing the risk to ecosystems and once in the human body can cause various types of cancer.8

Motivation

The information that led us to choose this project is the lack of specific systems to address the problem of microplastics pollution, given that Switzerland plays a substantial role as a contributor to this issue.3 We found out that the problem is also present in our country thanks to a study carried out by Oceaneye, a Geneva-based non-profit association that works to improve the health of aquatic environments, which analyzed the pollution of Lake Geneva by measuring microplastics on its surface. They analyzed 51 samples from different sites and found microplastics such as low density polyethylene (LDPE), high density polyethylene (HDPE) and polypropylene (PP) in all of them (Figure 2). In addition, Switzerland consumes three times as much plastic as other European countries, but recycles 30% less.5 By interviewing the director and the head of operation of the ERM Morges wastewater treatment plant (WWTP), we discovered that there are no treatment systems that specifically target microplastics to prevent them from entering our lake. In fact, even though some of them are retained in the WWTP sludge, microplastics still pass trough the treatment plant and end up in the lake. To tackle this issue, we decided to develop an innovative, eco-friendly and cheap solution using synthetic biology.

Lake geneva site containg microplatics
Figure 1: Numerical concentration of accumulated micro- and mesoplastics in [particles/km2] in lake Geneva, from the "Assesment of pollution of lake Geneva by micro- and mesoplastics surface wastes" study report done by Oceaneye.
microplastics pathway
Figure 2: Entry points of plastic in Lake Geneva. Microplastics are everywhere in the environment and enter water bodies in various ways. Some of them come from the degradation of larger objects that are made of or contain plastics, such as packaging, tires or synthetic fabrics that lose microfibers when washed. Other microplastics are manufactured directly by industry and are used, for example, in cosmetics. This figure was made using Canva.

Our Solution

Our aim is to prevent microplastics from entering water bodies by capturing them upstream. To address this, we decided to induce overexpression of the Curli fiber in a strain of E. coli to overproduce biofilm. Leveraging the natural adhesive properties of this natural biomaterial, we aimed to bind all types of microplastics. However, after discussing with various experts, we further developed the project in two areas. First, in order to capture the most prevalent types of plastics, which are polypropylene (PP), polyethylene (PE) and polystyrene (PS), we decided to functionalize the Curli fibers of our biofilm with peptides that bind specifically to these types of plastic.
Secondly, we found out that rubber particles resulting from the abrasion of tires on the road are passing through grids and drains with no suitable filtration system to retain them, and are therefore being discharged directly into the lake. Since the idea of improving the biofilm specificity through protein domains with affinity for different materials was promising, we decided to include in our tool box a component that would specifically capture these tire particles, and added a rubber-binding domain to the Curli fibers.
(see section Design)
Our engineered Escherichia coli biofilm, functionalized to capture microplastics, could be implemented at multiple levels, including wastewater treatment plants, road drains, and washing machine filters.
(see section Implementation)


image of biofilm
Figure 3: Biofilm that captures microplastics. We engineered our biofilm by functionalizing the Curli fibers with peptides and a Rubber-binding domain in order to capture microplastics.

References