Article: Ethylene vinyl acetate polymer as a tool for passive sampling monitoring of hydrophobic chemicals in the salmon farm industry. Marine Pollution Bulletin, 88 (2014) 174–179. DOI: 10.1016/j.marpolbul.2014.09.009
Sea lice and Antiparasitics
Sea lice are parasites that feed on the tissue, muscle, and blood of marine fish. A large group of parasites feeding on one fish can cause serious or even fatal problems. Fin damage, skin erosion, constant bleeding are possible consequences of parasites attack.
Caligus rogercresseyi has become a major parasite of concern on salmon farms in Chile. The Chilean Fisheries Service implemented an Official Surveillance Program in the main salmon production area of southern Chile to assess the situation of sea lice in fish farms. Results showed an increase in the number of positive cages and cage-level abundance of sea lice in southern Chile since 2004. The prevalence of sea lice in the fish farms was 53.4%, and the average sea lice abundance was 11.8 per fish.
In order to have control over parasites, synthetic pyrethoid has been invented and put into use. Cypermethrin is a hydrophobic pyrethoid (hydrophobic means something prefers going into organic phases for example lipid than staying in water) taking effect at low concentrations. It bounds to particles in the water column and can endure long range transport. Although spread over salmon farm with a purpose of killing parasite, it is released to the ocean after 60 min treatment and has the potential to harm non-target organism, such as copepods, benthonic crustaceans and mussels.
Method and Results
Tucca used polymer ethylene vinyl acetate (EVA) for monitoring the concentrations of cypermethrin in the salmon farm industry. EVA is an additive to our daily used plastics. Because of the preference of cypermethrin to stay in EVA than in the water, EVA can serve as a tool for collecting pyrethoid in the aquatic environment. It is cheaper and easier to handle than actively collecting large quantities of water.
EVA were dissolved into dichloromethane and coated onto glass fiber filter. They were then deployed into Manai Bay in some stainless steel baskets for 7 days and sent back to lab for extraction and analysis. EVA samplers demonstrated that the average concentration of cypermethrin in the water was 2.07 ± 0.7 ng/L close to salmon cages, while near-shore was 4.39 ± 0.8 ng/L. Fast current speeds could explain the lower concentration near salmon cage.
This study revealed a concentration level of cypermethrin closer to the threshold of toxicity. For example, shrimp Mysidopsis bahia has reported lethal concentration in 50% of tested organisms (LC50) at 5 ng cypermethrin per liter of water, after 96 h of exposure. However, since the deployment was conducted within a treatment period, the concentration would drop from dilutions after the cypermethrin treatment ceased.
Passive sampling provides a low-cost and easy handling way for organic pollutants monitoring. It has the potential to be applied to other common organic compounds released from salmon farm activity, for instance, antibiotic and disinfectants. It offers us with access to the on-time monitoring of these compounds in the aquatic environment and helps to prevent serious harm to marine organisms.