Where have the eels gone

Keskiviikko 18.1.2023 klo 14:51 - Mikko Nikinmaa

Everything was better in the past. That is the slogan of conservative populists throughout the world. It is actually true for some things, but the actions should be completely different from the ones advocated by the populists in order for us getting the good things from the past also in the future.

Here I am focussing on the eel. Smoked eel is a true delicacy. When I was a child, one got eels virtually every time one went fishing. The fish was fatty and had virtually no bones making it tasty and easy to eat. However, eels started disappearing from the shops and waters from 1970’s onwards and now you can rarely find them anywhere.

The life cycle of the eel is the main reason why the species is so vulnerable to environmental contamination. The European eel stocks have decreased more than 90 % from 1970’s to 2010’s. If one starts from the sexually mature eel, it migrates several thousand kilometres from the inland waters, where it matures, to the spawning site in Sargasso Sea. During this months-long migration the fish does not eat, but uses the fat deposits as energy stores. This fact has several consequences. First, the condition of eels reaching the spawning site is poor. Many do not make it to the site at all, and the rest are barely able to make the final effort of the spawning migration. Any lipid-soluble environmental contaminants are released to the circulation when lipid deposits are used for energy production. This further weakens the fish. Also, because of the climate change, the ocean currents may have weakened causing an increase in the energy consumption during swimming from Europe to Sargasso Sea. This also weakens the eel before spawning.

The adult eels die after spawning, but the developed embryos start their long travel towards the European feeding grounds. No specific problems have been found in the early part of the migration in the Atlantic. However, it is possible that the food items of the eel embryos have decreased in abundance and that ocean currents have slowed down. When the eels come to the European coasts, a final strenuous part of the travel awaits. They must go up to suitable growth sites. In selecting where to swim to, eels use, e.g., the lateral line organ. This sensory organ is very sensitive to metal contamination. Thus, the present increases of copper, lead and cadmium levels may disturb the final leg of eel migration.

In short, eels suffer from environmental contamination in most parts of their migration. Further, the studies have shown that the presently occurring contaminant levels are adequate to cause, e.g., sensory problems. Consequently, to be able to go back to the good old days, when smoked eel was a common delicacy, we need to improve water quality.

Kommentoi kirjoitusta. Avainsanat: aquatic toxicology, metal pollution, climate change

Decreased oil use influences climate change in two ways

Keskiviikko 8.6.2022 klo 20:22 - Mikko Nikinmaa

Oil spills are among the biggest toxicological problems in marine environments. Although the news pictures invariably show oil-covered birds, which die of heat loss in water, oil components are also very toxic to all aquatic organisms. The decrease in the use of fossil fuels will decrease the tanker transport of oil, oil leaks in the harbours of oil refineries, and accidental or intentional oil spills from ships. The net result is that oil pollution will diminish. Although only the importance of oil burning is usually considered as being important in combatting climate change, the decrease in oil pollution must also be considered. The fact is that marine algae carry out about half of the carbon dioxide removal and oxygen production by photosynthesis. Algal photosynthesis has decreased by 10-20 % because of marine pollution. This decrease is so far greater than what has been caused by deforestation of rainforests. The main pollutant causing algal deaths is oil and its components. Thus, decreasing the oil use will combat climate change not only directly but also as decreased oil pollution enables algal photosynthesis to recover. As a consequence, oil ban will have greater positive effect on climate than expected from decreased carbon dioxide production because of oil burning.

Kommentoi kirjoitusta. Avainsanat: aquatic toxicology, oil pollution, algal photosynthesis

Environmental Pollution Accentuates Problems of Hypoxic Fish: Why?

Maanantai 20.9.2021 klo 14:55 - Mikko Nikinmaa

Hypoxia, i.e., low oxygen concentration, has increased in aquatic environments throughout the world. Hypoxia is mainly caused by eutrophication of waters whereby the oxygen consumption of organisms (but also oxidation of dead materials) increases. The occurrence of hypoxia is either continuous or diurnal. Diurnal changes in oxygen levels occur, if the eutrophication is mainly resulting from the increased biomass of photosynthetising organisms: during the day, when light is available, the increased photosynthesis can cause the environment to become hyperoxic, while at night even those organisms only respire, whereby the oxygen level drops. Continuous hypoxia occurs, when the oxygen demand always exceeds its diffusion (especially from the air) and production.

Fish take up the oxygen they need via the gills. The gills are also the major site of acid-base and ion regulation. This dual function has generated the “osmorespiratory compromise”:   high functional surface area and low diffusion distance favour oxygen uptake, whereas low functional surface area and high diffusion distance favour ion regulation. Aspects of this have been reviewed by Wood and Eom in Comparative Biochemistry and Physiology A-Molecular & Integrative Physiology 2021 Vol. 254 (DOI: 10.1016/j.cbpa.2021.110895). From the environmental pollution point of view, it is important to note that many if not most pollutants have important effects on gills.

Because of the effects of pollutants on gills, it can be expected that the hypoxia responses of fish are affected by pollutants. This is all the more worrisome, as the same sources are the cause of both eutrophicating nutrients and many toxic wastes, i.e., water that has gone through wastewater treatment plants. Lau et al. have studied, how hypoxia responses of fish vary in clean water and in effluent from a modern wastewater treatment plant (Lau et al. Environmental Pollution 2021 Vol. 284, DOI: 10.1016/j.envpol.2021.117373). They observed that the hypoxia tolerance of fish was markedly decreased. This was associated with a reduction in the decrease of the so called intralamellar cell mass. Recently, it has been found that fish increase the functional area of gills in hypoxia largely by decreasing the intralamellar cell mass. If this cannot be done, hypoxia tolerance is impaired. It is not known, why the intralamellar cell mass could not be reduced in the effluent-treated fish. However, the results clearly show that the osmorespiratory compromise of the gills is an important factor to be taken into account when the success of fish in polluted, hypoxic environments is studied.

Kommentoi kirjoitusta. Avainsanat: aquatic toxicology, water pollution, gill function, hypoxia

Disruption of rhythms - a significant toxicant effect

Tiistai 20.4.2021 klo 17:25 - Mikko Nikinmaa

Virtually all animal functions are rhythmical. If you measure a parameter, the value is different in the morning than in the evening or in the summer and in the winter. Despite this fact, the rhythmicity is seldom taken into account in considering the effects of toxicants on animals. We have earlier published an article indicating the importa


nce of disturbed rhythms in environmental responses (Prokkola and Nikinmaa Journal of Experimental Biology, 2018, 221, jeb179267). Now in Environment International (149,  106159, 2021) Zheng et al reviewed how “Environmental chemicals affect circadian rhythms: An underexplored effect influencing health and fitness in animals and humans.”

Zheng et al showed how tens of environmental toxicants including pesticides, steroids and metals can be considered circadian disrupters. Thus, the toxicants cause disturbances if normal rhythms. Considering this, the responses to toxicants will disturb the daily and seasonal rhythms of animals. Since the rhythms are an important 

aspect of animal fitness, the circadian disrupters will affect the success of animals. At the moment the rhythmical responses are further disturbed as the light-temperature relationship is altered by climate chang

Kommentoi kirjoitusta. Avainsanat: circadian disruptors, aquatic toxicology

Aquatic microplastics, not necessarily a problem

Tiistai 25.8.2020 klo 18:18 - Mikko Nikinmaa

Indigestible fibers are considered to be good for you. Such fibers enter your alimentary canal and pass through it without any changes, nothing is taken up in the gut. However, they help in the motility of the gut, and some materials, which are indigestible to us, can be utilized by gut microbes. Regardless, if material is going through your gut without anything taken up, it is inert and if its dimensions are such that it is easily transferred through the gut, cannot be considered harmful. The same is true for all animals.

So, fibers are good for you. If I changed the word fiber to microplastic, then people would start screaming about terrible poisons. Headline news almost everywhere in the world feature every once in a while stories about how these terrible microplastics are found in fish and other seafood, and can therefore be transferred to you. But if the dimensions are correct, the microplastics can be just like any other inert material going through the alimentary canal. Many plastics are nowadays made such that they meet foodstuff packaging requirements. If these plastics are broken down or if microbeads are produced from such plastics, they are completely harmless. We have been drinking water and soft drinks in plastic bottles for tens of years without being poisoned by microplastics, although every time we drink, we digest microplastics. So, in principle, microplastics are not a problem, if the material is foodstuff quality.

Microplastics can, however, be a problem. First, there are many types of plastics, some of which contain toxic components. Currently, about half of all the microplastics entering water are particles from tire wear. With the current traffic situation, there is very little one can do to this type of contamination. This is in contrast to microplastics in wastewater treatment plants, where more than 95 % of plastics are retained. The tire plastics have toxic components. Second, most of the toxic compounds are hydrophobic. Therefore, they adsorb on plastic particles, and will easily diffuse to organisms through the hydrophobic lipid gut walls. In this case it is not the microplastics themselves which are toxic, but the toxic compounds that have found their way to the environment. By stopping the release of these toxicants also the toxicity of microplastics would disappear.

The problem is that by focusing on microplastics in the aquatic environment, one is not addressing the real questions: decreasing road traffic (thus decreasing tire wear particles), decreasing toxicant release (thus decreasing toxicant adsorption and transfer into organisms) and completely stopping the use of toxic compounds in plastics.     

Kommentoi kirjoitusta. Avainsanat: plastic pollution, aquatic toxicology

Aquatic Oil Pollution ? many-sided problem, until oil use is stopped

Torstai 18.7.2019 klo 11:44 - Mikko Nikinmaa


With oil spills, the usual picture in the news is a bird covered with oil. The contaminated bird loses its ability to regulate temperature in water and slowly dies because of heat loss. Although this is a significant problem during oil spills, it is probably not the most important one. As the most important one I would place the effect of oil contamination on mainly unicellular marine algae. Marine algae account for almost half of global photosynthesis, thus being the most important carbon dioxide sinks of the world. Largely because of oil pollution, it has been estimated that the algal carbon dioxide sink has decreased by 20 %. This negative effect is greater than would be caused, if deforestation of Amazon rain forest would increase manyfold. Oil pollution also influences fish. Effects are largely age-dependent and associated mainly with cardiac function. It appears that the toxicity of oil increases with increasing pressure. This is significant, as oil is drilled at deeper depths than earlier. In addition, dispersants, changing oil to small droplets, which are dispersed in the water column, increase the toxicity of oil spill to fish and other aquatic organisms, mostly by increasing the surface area of oil in contact with the (respiratory) surface of organisms. As a consequence, the uptake of toxic components of oil, and thereby their toxic effects, are increased. In contrast, the dispersants in the concentrations used appear to cause little toxicity. It is quite clear that as long as oil is used in significant amounts in fuels and energy production, the problems persist. Further, the socalled biofuels or biodiesels are exactly as bad for aquatic life as fossil oil. Therefore, in terms of combatting climate change, using biofuel is exactly the same as using fossil oil, if the use of fossil fuel is coupled with forestation.

Kommentoi kirjoitusta. Avainsanat: aquatic toxicology, oil spill, water pollution, fish kills

SETAC (Society for Environmental Toxicology and Chemistry) in Helsinki 26.-31.5.

Sunnuntai 26.5.2019 klo 13:26 - Mikko Nikinmaa

This coming week more that 2000 environmental scientists meet in Helsinki discussing many different aspects of environmental contamination, starting from indoor air quality ang going to endocrine disruption in wildlife. Presentations include those on nanotoxicology, plastic pollution and climate change. Thus, pressing environmental problems are handled by a wide internationel group of experts. My personal input in the meeting is a session on individual variation in toxicological responses, which I wll discuss here later.

Kommentoi kirjoitusta. Avainsanat: environmental polllution, aquatic toxicology