The health of unborn babies and young children is at risk due to mercury pollution. Children's brain development can be harmed by exposure to mercury when it washes into lakes and streams, as well as adults who eat seafood. Health and reproduction in fish and other wildlife are at risk due to the use of mercury.
Humans, animals and birds are exposed to mercury when they eat seafood. Scientists have been studying how and when fish accumulate mercury. This information is used to assess mercury risks across different water bodies and landscapes.
Scientists have used fish ear stones to gain insight into fish growth, migration, diet and the timing of their exposure to certain pollutants. The tiny structures of calcium carbonate help regulate hearing and balance in fishes. Predicting how climate change is affecting fish is possible with the help of otoliths.
Mercury is not included in otoliths. They bind very strongly to tissues that are sulfur-laden. In the past, muscle tissues have been used to assess mercury pollution.
A new window into individual fish's lifetime exposure to mercury can be seen by measuring it in the fish's eyes. It is possible to understand fish lifetime exposure to this potent neurotoxicant.
There are clues in fish ears.
Scientists measure mercury in fish by measuring how much it accumulates in the whole body of the fish or just in the filets. The approach tells us how much mercury the fish has accumulated over time, but it doesn't tell us when the fish was exposed. There is a time stamp that is missing.
Depending on the fish species, mercury concentrations can vary. The US government monitors mercury levels in cod from 1991 to 2010 and they ranged from low to high. Changes in mercury emissions over time can affect an individual fish's exposure.
A new method for assigning ages to fish eye mercury concentrations is proposed in our study. It is possible to take up mercury directly from water or from the fish's diet if you wear eye glasses that are high in sulfur.
The substance is preferentially taken up in certain parts of the body. It can affect fish vision at high levels.
The technique of aging a fish using its otolith has been used for a long time. The yearly layers of calcium carbonate are added to the fish's otolith. Foresters date trees by measuring the growth rings in their trunks, so we can estimate the fish's age and growth rate by measuring the distance between the annual growth layers.
The growth of a fish's otolith is related to the growth of its eye. The distance that we found in the fish's otolith was applied in our analysis. The linear relationship between the two measures is strong for the Round Goby.
This correspondence with the otolith can be used to determine when the fish was exposed. The chronology of lifetime exposure can be followed because the fish's eye lens grows over time.
The new method will allow us to trace the mercury exposure of a fish. Questions can be asked about how life history events, such as migration and diet shifts, or temporal events such as low dissolved oxygen levels in water, may affect a fish's mercury levels.
The strength of this method is that it provides information for individual fish. Different fish have different abilities and can affect their growth and exposure to mercury.
Having information about mercury exposure for all ages of a single fish can help decrease the need to collect large samples of many fish across all ages, which is how scientists traditionally have assessed how fish's exposure changes over their lifetimes.
Climate change may affect mercury exposure.
Some of the dissolved oxygen in the water is being lost. Deoxygenation is an important stressor for aquatic life.
Hypoxic conditions can be associated with elevated concentrations of methylmercury when oxygen in a pond or bay is less than 2 milligrams per liter. The loss of oxygen is worsened by pollution from farms and cities. Warming can cause it to happen in the open ocean.
Increasing hypoxia could make the mercury that is already in lakes and oceans more available for use in fish. Individual and species responses to hypoxia can be different. Our current research is funded by the National Science Foundation and is looking at how fish eye lens and otoliths can help us get rid of mercury from our diet.
Scientists are starting to realize that body parts of organisms are archives of the past. Eye glasses and otoliths are used to understand the lives of individual fish.
The Environmental Science and Technology Letters has more information on this. The book is titled "acs.estlett.2c00755."
Journal information: Environmental Science & Technology Letters
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