TRACKing of PLASTtic emissions from aquaculture industry

The objectives of this study were: 1) to acquire knowledge about aquaculture related release of plastic and microplastic to the marine environment; 2) to identify and determine relative amounts of specific microplastics in the water column, suspended matter and seabed, in the immediate vicinity of an aquaculture farm; 3) to evaluate which aquaculture processes are the potential sources of identified microplastics in the environment. This study will provide a scientific basis for the development of an action plan to reduce plastic emissions from the seafood industry.

To achieve these goals, raw materials and ingredients currently used for fish feed production as well as the finished product were collected along with environmental samples of seawater, marine sediments and suspended matter near a salmon production site. Gills and GI-tracts of farmed and wild salmon were collected, to estimate the potential exposure of aquatic life to plastic particles originating from aquaculture activities. Furthermore, the abrasion effect induced in the feeding pipes during the distribution of pelleted fish feed was experimentally simulated. This contributed to the understanding of both the role of the aging of the plastics pipes as a relevant factor in the fragmentation pattern, as well as to preliminarily characterize the grain size distribution of the particles potentially released from the feed pipes, during normal aquaculture production. Mass spectrometry analyses indicated microplastic (MP) contamination in some of the analysed raw materials used for feed production and finished feed. Amounts of MP were in the range of a few µg/g of polyethylene (PE) and polyamide (PA) in fish meal and polypropylene (PP) in the finished product. Investigation of the wheat gluten production line helped to identify a primary source of the PP release and actions are suggested to eliminate this source of contamination. Particle analysis of the same material identified a few PE, PA and polyethylene terephthalate (PET) particles (21-38 µm) as the major contribution of the MP contamination. A large fragment of PP, and minor occurrences of other polymer types such as PA were also found. In total 10 polymer types accounted for 95% of the polymer composition in feed. PE and polystyrene (PS) displayed higher concentrations at the sites close to the cages, while all the remaining investigated polymer types had no clear area related distribution relative to aquaculture activity, i.e. the reference site in the study showed a similar pool of polymers, often with similar levels of accumulation. In suspended matter, the total amount of particles was 220 000-360 000 particles/kg of dry weight, around 1000 times the concentration of the bottom sediment samples. PET, PP and PA were the dominant polymer types. In water samples the concentration of particles over 10µm were analysed using pyrolysis GCMS (Pyr-GCMS). PE, PS and PET were the dominant polymer types. PE displayed higher concentrations at the sampling sites close to the cages. The obtained results should be interpreted as preliminary indications in the complex assessment of emissions of MP from aquaculture activities.The qualitative results of histological analyses in the gills of farmed salmon showed the presence of MP (5 to 25 µm particles) in the lamellae of gills of slightly more than half of the sampled fish, and the mass spectrometry analysis identified the presence of PE in the same samples. As simulated during an experimental activity within this study, the abrasion of the PE containing feed pipes during the aquaculture production and the consequent release of microns sized MP may suggest that the pipes are a source of the identified PE microplastic.