What is H2S?
Hydrogen sulfide H2S is a colourless gas with the characteristic smell of “rotten egg” at low concentrations. The gas is known as the “silent killer” as it is extremely flammable and toxic. H2S is produced in numerous industries, such as mining, oil and gas refining and paper processing. In addition, the gas also occurs naturally in volcanoes, sewers, oil and gas wells and well water .
What is RAS?
Recirculating aquaculture systems (RAS) are land-based aquaculture facilities where fish are farmed in tanks where the water is recirculated. The use of RAS gives control over many parameters that play a part in fish welfare, such as pH, temperature and dissolved oxygen, and RAS thus has potential in maintaining high fish health. In Norway, these facilities are used for both producing food fish and rearing smolt. Since we are a nation where fish farming is a vital industry, it is important that these facilities perform optimally.
Why is H2S a problem in RAS?
The RAS sector is currently facing the problem of hydrogen sulfide toxicity, which is harmful to fish, and in some cases results in acute fish death . H2S production occurs when sulfur bacteria in the tank forms biofilm where the environment is anaerobic. Should H2S toxicity lead to fish death in RAS facilities, it goes without saying that the resources put into rearing the fish go to waste. Even if death does not occur, the stress of H2S poisoning over time decreases fish welfare.
Non-optimal detection systems
Industry stakeholders report that sensors available today do not have sufficient sensitivity, or are not reliable to detect the concentration of H2S before it reaches a toxic level. The ones that do have some level of reliability are very expensive, and it is therefore a high threshold for companies to invest in such a sensor.
We propose SulFind as a solution, a biosensor that will have high sensitivity to H2S, and offer continuous monitoring. Our sulfide sensor will work as an alarm-system when the concentration of H2S is approaching a toxic level. If H2S levels are monitored, RAS facilities can increase the inflow of water when H2S levels rise, diluting the water and preventing disaster from striking. Therefore, a sensor may be used preemptively against H2S poisoning. It is however important to note that the most important preventative measure against H2S is tank cleanliness. Our sensor should not be used in lieu of proper tank cleanliness, but rather as an additional measure to combat H2S in RAS.
Why use synthetic biology?
Although there are other solutions to the H2S toxicity, these have proven to be insufficient in regards to both the industry’s wishes and needs. With synthetic biology it is possible to detect H2S at much lower concentration than existing methods, and therefore prevent acute fish death and profit loss. In our proposed implementation the biosensor will never be in direct touch with neither fish nor humans, and with the correct biosafety measures this biosensor should be ethically responsible.
What we strive towards
In our iGEM project, we aim towards successfully designing a biological system that detects sufficiently low concentrations of H2S to prevent acute fish death. Furthermore, our goal is to embed this biological system onto a microfluidic chip that will be implemented in a RAS facility. Besides our technical aspirations, we strive towards contributing to a more sustainable fish farming sector where fish welfare is maintained. If our project succeeds, we hope our contribution provides more favorable conditions for land based fish farming.
Since Norway is the second largest exporter of fish and seafood, it was natural for us to look towards the fish farming sector to find our problem. After meeting with several researchers at Norwegian universities such as NTNU and UiB (University of Bergen), we gained insight into the problems H2S causes in RAS facilities and the need for a biosensor. Further contact with stakeholders within the industry confirmed this insight, and heavily influenced us to try to solve this particular problem.
 Occupational Safety and Health Administration. Hydrogen Sulfide: Overview. U.S. Department of Labor. Retrieved 18.08.2021 from: https://www.osha.gov/hydrogen-sulfide
 Thomsen, A. E. (November, 2018) Akutt fiskedød i RAS-anlegg bekymrer forsikringsbransjen. kyst.no. Retrieved 18.08.2021 from: https://www.kyst.no/article/akutt-fiskedoed-i-ras-anlegg-bekymrer-oss/