Potential environmental impact of bromoform from Asparagopsis farming in Australia

To mitigate the rumen enteric methane (CH4) produced by ruminant livestock, Asparagopsis taxiformis is proposed as an additive to ruminant feed. During the cultivation of Asparagopsis taxiformis in the sea or in terrestrial based systems, this macroalgae, like most seaweeds and phytoplankton, produces a large amount of bromoform (CHBr3), which may contribute to ozone depletion once released into the atmosphere. In this study, the impact of CHBr3 on the stratospheric ozone layer resulting from potential emissions from proposed Asparagopsis cultivation in Australia is assessed by weighting the emissions of CHBr3 with the ozone depletion potential (ODP), which is traditionally defined for long-lived halogens but has been also applied to very short lived substances (VSLSs). An annual yield of ~3.5 × 104 Mg dry weight (DW) is required to meet the needs of 50 % of the beef feedlot and dairy cattle in Australia. Our study shows that the intensity and impact of CHBr3 emissions varies dependent on location and cultivation scenarios. Of the proposed locations, tropical farms near the Darwin region are associated with largest CHBr3 ODP values. However, farming of Asparagopsis using either ocean or terrestrial cultivation systems at any of the proposed locations does not have potential to impact the ozone layer. Even if all Asparagopsis farming was performed in Darwin, the emitted CHBr3 would amount to less than 0.016 % of the global ODP-weighted emissions. The remains are relatively small even if the intended annual yield in Darwin is scaled by a factor 30 to meet the global requirements, which will increase the global ODP-weighted emissions by 0.48 %