Methylmercury Research

June 2020

Cawthron scientists develop a significant test for methylmercury in fin fish

The Cawthon Institute and New Zealand Food Safety are collaborating with Crown Research Institute ESR on pro-active research to protect market access for New Zealand’s fishing sector by developing techniques to quickly and accurately measure levels of methylmercury in fin fish populations, so consumers can be confident the seafood they eat is safe to eat. One significant test for methylmercury has been developed by scientists at the Cawthon Institute and is about to be internationally accredited.


At the Cawthron Institute, Dr Tim Harwood’s research interest includes the accumulation of natural toxins in food from both marine and terrestrial environments. His work as the Safe NZ Seafood Programme Leader has involved working with Cawthron scientists like Analytical Science Technical Officer Geoff Miles, to develop techniques and establish levels of methylmercury in New Zealand’s fish that we consume and export.


Finfish and other seafoods are rich sources of minerals and vitamins and they contain many health-promoting elements. However, some seafood can contain harmful toxins of one variety or another and it is important to be able to identify those, without discouraging consumers from enjoying the considerable nutritional benefits of eating seafood.


Methlymercury (MeHg+) is a health risk for humans. It is the predominant form of mercury in marine species, making up approximately 80% of the total mercury present. Methylmercury is particularly toxic amongst the different types of mercury. It affects enzyme function, protein synthesis and, because it is able to cross the blood-brain barrier, it can cause a number of serious human health issues. For example, toxic levels of methylmercury affects foetal brain development if consumed during pregnancy.


Mercury is a naturally occurring heavy metal that is released into the atmosphere through natural environmental processes such as volatilization of natural deposits and volcanism, and human activity, such as industrial processes, coal burning and the use of some fertilisers. It eventually falls to the ground or into water and is bioaccumulated by animals up through the food chain, as predators feed on smaller prey that have themselves ingested plants or smaller prey that have been exposed to mercury. New Zealand’s relative isolation does not make us immune to its effects. This is a global issue.


Until recently most studies have tested for total mercury and there has been little research on how methylmercury in New Zealand fish species. Testing methylmercury is important to ensure the guidance offered around eating fish, especially during pregnancy, is robust and also to support the process of setting international standards. These standards balance the risk of exposure to methylmercury against the extensive, positive health benefits of consuming fish. 


The work is a collaborative effort between the fishing industry, New Zealand Food Safety ( a business unit of MPI), ESR (the Institute of Environmental Science and Research) and the Safe NZ Seafood programme at the Cawthron Institute. Dr Andrew Pearson, manager at New Zealand Food Safety, says the work being undertaken at the Cawthron is a pro-active response to a growing international interest in determining the safety of food.


Fish samples have been collected by Fisheries NZ observers and prepared by ESR for further analysis at the Cawthron. New Zealand Food Safety worked with Seafood New Zealand, captains of fishing vessels and MPI fisheries observers, to make sure representational samples of relevant fish species, different sized fish within a species type and gathered from different locations, were included in the study.


New Zealand fish under scrutiny include two key export species, ling and orange roughy. These are important to our export industry as they are certified sustainable export species. Additionally, species such as barracouta, gem fish, and smooth and black oreo have been included as comparison species.


The overall research programme instigated by New Zealand Food Safety is currently about two-thirds of the way to completion. The next step is to collate the Cawthron research with that being done at ESR. Dr Pearson says as a result of the methods developed and the science undertaken at Cawthron, consumers can be confident in the results of the survey and in the guidance that will ensue as a result. 


Dr Tim Harwood explains the work at Cawthron included developing the methylmercury test and applying it to the fish survey. Three hundred fish samples from six species were analysed. The results will be entered into the WHO Global Environment Monitoring System – Food Contamination Monitoring and Assessment Programme (or GEMS/Food) data base. In the very near future, the Cawthron-developed methodology is poised to become internationally (IANZ) accredited, enabling internationally recognized reports to be generated and used as a result of this work. 


The method has been further validated and is able to test a range of wild-caught species. This adds to suite of analytical tests for industry, such as iodine level, omega fatty acids and protein content. Eventually, all information will be made commercially available to importers and exporters of fish.


Showdown Productions Ltd – Rural Delivery Series 15 2020