Pollutants in glaucous gulls

Last updated 17 August 2016

The glaucous gull (Larus hyperboreus) is at the top of the food chain and exposed to excessively high amounts of persistent organic pollutants. It is the most abundant of the large gulls in the Arctic, and its important food items are benthic fauna, fish, carrion, and eggs and chicks of other seabirds.

Status and trend

The levels of organic pesticides like HCB and oxychlordane have dropped during the 18 years the glaucous gulls have been monitored. However, there are substantial variations from year to year. These variations mean that it is too early to draw any final conclusions regarding the trends, but since the trends coincide with the ban on the use and discharge of the pollutants, it is most likely that the average reduction is real.

The concentration of DDE, the breakdown product of the insecticide DDT, also varies considerably from year to year. It is not possible to say whether the DDE levels in glaucous gulls are rising or falling. This is actually surprising because the use of DDT was banned in most western countries already in the 1970s. However, some DDT is still being used to combat the malaria mosquito in southern parts of Africa following a recommendation from the World Health Organisation (WHO), but it is uncertain whether any of this can be found in the Arctic. Another possible reason may be that the levels had already declined before the measurements began and the speed of the reduction has flattened out. The proportion of DDE is still high compared with the other pollutants known to be present in glaucous gulls.

The PCB level is presented in MOSJ as the concentration of PCB-153, the most stable variant of the 209 possible PCBs. There is a very good link between PCB-153 and the other PCBs. The concentration of PCB-153 therefore gives a correct picture of the development of the PCB levels in the glaucous gull.

There was some variation in the concentration of PCB-153 during 1997–2009, but on the whole the levels halved during this period due to the regulations that were introduced. New uses for PCB were banned in most western countries in the early 1980s. Many countries also put an emphasis on proper waste handling and disposal when dealing with PCB in rubbish during the phasing-out period, which was probably important since very large quantities of PCB were used in many products.

PFASs (PFOS and PFOA) have been produced since the 1950s due to their desirable physico-chemical properties, but it is only relatively recently that they have become the focus of scientific investigation. After PFOS was detected in wildlife, its main producer initiated a voluntary phase-out in 2001. The reduction seen here is thus likely a continuation of a longer time period of decreasing levels of PFOS in wildlife. PFOA has been proposed for inclusion in the Stockholm Convention and is therefore an important contaminant to focus on. The data herein show a reduction of both PFOS and PFOA levels in glaucous gull eggs from Bjørnøya and Kongsfjorden. There is a considerable difference in PFOS concentrations between eggs from Bjørnøya and Kongsfjorden and the specific reason for this is currently unknown. However, glaucous gulls from Bjørnøya are likely exposed to higher concentration of PFASs through their diet which is then transferred into the eggs.

Causal factors

The high levels of “old” organic pollutants like PCB-153, DDE, oxychlordane and HCB, and at times high values of “new” pollutants like  perfluoroalkyl and polyfluoroalkyl substances (PFOS and PFOA) are mainly caused by 2 factors:

1. The glaucous gull is at the top of the food chain. These pollutants are stable and are slowly broken down in nature. The pollutants entering the food chain therefore become more concentrated as the animals eat (bioaccumulation). When these animals are eaten by the next ones in the food chain, further accumulation takes place. Hence, the levels of stable pollutants increase up the food chain. The difference in the concentration at each level in the chain varies considerably from one pollutant to another, and in the food chain in the Barents Sea it is from around one to more than 2000. This is due to the physico-chemical properties of the compounds.
2. Glaucous gulls have limited ability to convert and rid themselves of them through their faeces.

Consequences

The high levels of pollutants recorded in glaucous gulls from 1997 to 2013 have had considerable consequences for the health of the glaucous gulls on Bjørnøya in the Barents Sea.

Some of these glaucous gulls eat large numbers of seabirds, eggs and chicks during the breeding period and these individuals are particularly likely to have the highest levels of pollutants. The most pronounced effects have been found in these birds, but negative effects have also been seen in birds away from Bjørnøya.

Effects have been found on the enzyme, immune and hormone systems, reproduction and survival. The significance of these effects is, nevertheless, still uncertain, but as so many negative effects have been found in the same population there is little reason to assume that this does not have a negative impact on the health of the glaucous gulls. Modelling has also shown that pollutants probably have negative effects on the glaucous gull population on Bjørnøya.

Glaucous gulls which have been found sick, dying and dead on Bjørnøya have had extremely high levels of pollutants.

There are probably several natural causes for the death of glaucous gulls at their breeding sites, including old age. However, studies show that the ability to find food may be reduced with increasing concentrations of pollutants. This means that individuals with a high level of pollutants may starve and thus decline in weight. A drop in weight means that fat is consumed which, in turn, raises the concentration of pollutants since they are in the fat. Consequently, pollutants may contribute to a negative “spiral effect”, whereby poor availability of food gives increased pollutant concentrations which, in turn, make the individual less able to find food, ultimately resulting in it dying due to shortage of food and poisoning.

As the glaucous gull is a top predator in the arctic system and is exposed to high levels of pollutants, it is important to follow the trend in pollutant concentrations over time to assess the health of the glaucous gulls and verify that the international regulations concerning pollutants are working.

Samples from glaucous gulls are also often used to seek possible new pollutants.

About the monitoring

The glaucous gull is the most important, large gull in the Arctic. It has a circumpolar distribution, which means that it lives in arctic areas in Russia, Alaska, Canada, Greenland and Svalbard. The glaucous gull migrates southwards in winter, but not out of the Arctic. The majority of glaucous gulls from Svalbard migrate to the waters off Iceland and the southern tip of Greenland in winter. In summer, glaucous gulls are found in the northern part of the Barents Sea, from Bjørnøya in the south to Franz Josef land in the northeast.

Knowledge about pollutant levels in glaucous gulls provides knowledge about how pollutants become increasingly concentrated up the food chain and on possible effects in the top predators. The substances included in the monitoring are organic pollutants that are found everywhere in the environment even though many are no longer in use.

Research on glaucous gulls has uncovered effects of pollutants on the behaviour and the immune, enzyme, hormone and vitamin systems of the gulls. Individuals with the highest levels of pollutants have impaired reproductive ability and the survival of adults is lower. A general decline in the levels of phased-out pollutants is therefore positive for the glaucous gulls and the environment. Research to reveal whether known effects disappear with the decline of the “old” pollutants remains to be performed.

Further reading