Heavy metals were found in sea turtle eggs in record-breaking concentrations – according to a new Israeli study that may provide us with a broader picture of heavy metal pollution in the Mediterranean Sea.
Reut Alon, Zavit, Science and Environment News Agency
This year, I found a nest laid by a female sea turtle for the first time on one of the beaches in central Israel. For the past two years, I have been volunteering at the National Center for Sea Turtle Rescue, and discovering the miracle that occurred while they were sleeping was one of the most powerful and moving experiences I have ever had the privilege of taking part in. The eggs – which are no larger than a ping pong ball – are invaluable to those involved in the conservation of the sea turtles that live off our coasts. As part of the conservation efforts, many studies are being conducted, and one of them – which was also presented In the 52th Annual Conference on Science and the Environment which took place last September at Ben-Gurion University of the Negev – focused on turtle eggs, in which high doses of heavy metals such as mercury were found.
Two species of sea turtles nest on Israel's shores: the brown sea turtle and the green sea turtle, both in danger extinctionAbout 30 years ago, the National Center for Sea Turtle Rescue was established, operating under the Nature and Parks Authority, and efforts to conserve the marine reptiles bore fruit when last year registered Immigration In quantity The nests A female sea turtle comes ashore at dusk – usually on the same beach where she hatched herself – and uses her feet to dig a hole in the sand into which she lays her eggs, and when she is done, she returns to the sea.
A turtle that laid mercury eggs
The eggs are not only important for the survival of the species, but also for research. "There have been attempts in the past to use sea turtle eggs as a bioindicator for the presence of heavy metals in sea turtles," says Dr. Jack Silverman of the Institute for Marine and Lake Research, who is leading the study with his partners Dr. Mustafa Aspour of Ruppin College and Dr. Yaniv Levy, director of the National Center for Sea Turtle Rescue. "Naturally, the metals found in the eggs reflect the level of contamination in the turtle that laid them, and this can also give an indication of the situation in the sea."
Silverman and his colleagues' research focuses on detecting mercury in the eggshells of hatchlings (small sea turtles) after they emerge. "We're focusing on mercury because there's a general problem of mercury pollution in the Mediterranean," he says. Some of us know mercury as the liquid metal that used to be in household thermometers who were banned use for and distribution in the year 2015 Due to its toxicity, it has another state of aggregation – gas. "Mercury can be found in the atmosphere in a gaseous state, and reach the sea from there in the deposition of particles from the atmosphere such as dust or in precipitation such as rain."
However, mercury does not only reach the sea naturally. "Surprisingly, although the largest source of mercury is the sea as part of the overall mercury cycle in nature, the toxic metal also reaches the sea from human sources," says Silverman. According to him, burning fossil fuels such as oil and coal emits mercury in a gaseous state that evaporates into the atmosphere. In addition, the metal is released into the sea through sewage, or through countries in the northern Adriatic Sea and the western Mediterranean, such as Spain and Italy, which have a mining industry with a high concentration of mercury. "The Mediterranean Sea is a hotspot for mercury pollution because it is a relatively closed water basin, which has quite a few natural sources of the metal. In addition, there are also anthropogenic sources (human activities that affect nature, RA) such as industry and sewage that emit mercury into the atmosphere and directly into the sea."
The highest level
The current study focuses on spatial differences between the eggs laid in Israel’s southern, central, and northern regions – that is, it examines the concentrations of mercury in turtle eggs along the Israeli coast. “We are working to compare and examine the relationship between the concentration of mercury in the eggs and other parameters that we have information about from each nest – such as estimating the age and size of the [laying] turtle,” explains Silverman. “In addition, the assumption is that there is a relationship between her age and the amount of mercury she has accumulated over the years, so that an older turtle will probably have a higher concentration of mercury in the eggs she lays.”
The differences in mercury concentrations found in the eggs provide data not only on the turtle, but also on the different species of sea turtles that live in the Mediterranean Sea. According to Silverman, a brown sea turtle that feeds on other marine animals will have different concentrations of mercury in its eggs compared to the doses found in a green sea turtle that is mainly vegetarian. “The higher the trophic level of the animal – that is, the higher it is in the food web – the higher the mercury concentration will be,” he explains. “That’s why we found that the average mercury concentration in the eggs of brown sea turtles is higher than the average concentration we found in the eggs of green sea turtles.”
Moreover, this study is different in scope from previous studies that examined mercury contamination in sea turtle eggs. "In a similar study that was done in the past, the highest number of eggs tested was 30 – we sampled about 200 eggs from both brown and green sea turtles," says Silverman. According to him, a study done in Japan tested 6 brown sea turtle eggs, which had an average mercury concentration of 4.05 nanograms per gram of egg, the highest figure measured in the world – until the Israeli study.
And what data did we measure? "The average concentration we measured in brown sea turtle eggs was 9.3 nanograms of mercury per gram of egg," he says. "In green sea turtle eggs, we found an average concentration of 5.8 nanograms of mercury per gram of egg; we're talking about large differences of 2–3 times compared to the average of the highest concentrations found in green and brown sea turtle eggs in other studies around the world."
In addition to the average mercury concentration tested in all eggs of the various species, the maximum concentration and the average concentration in each nest sampled were also tested. According to Silverman, the researchers sampled about 10 eggs from each nest, and the egg with the highest concentration is the maximum figure. In addition, the average concentration for each nest was also calculated. "The highest maximum concentration we measured in one green sea turtle egg was 59 nanograms of mercury per gram of egg, and in a brown sea turtle we found 29 nanograms per gram," he explains. "For comparison, in a study from China that tested green sea turtle eggs, the maximum concentration found was 1.6 nanograms per gram – a small figure compared to the maximum concentrations we found here."
These are the highest values measured in a green sea turtle nest and a brown sea turtle nest, but Silverman notes that in the other nests tested, the maximum concentration was less than 5 nanograms per gram. "In two nests that we sampled in the Gedor Reserve, for example, the maximum concentration in one nest was 4.3 and the other was 3, and at Galim Beach we saw low maximum concentrations of 1.6 in one nest and 0.6 in the other nest," he says. The findings indicate variation from nest to nest and from beach to beach. "It is possible that high concentrations could be related to the size of the turtle or the area where it swims, but we don't have enough data on that."
According to Silverman, measurements on a small sample of 5-6 eggs, as was done in the past, cannot provide reliable information about the true level of contamination. "We want to get a more regional picture, so we turned to Dr. Yaniv Levy, director of the National Center for Sea Turtle Rescue, who is trying to obtain samples of eggs from various coasts in the Mediterranean for us," he explains. According to him, this study indicates some contamination that exists in the sea, and expanding it will allow for more uniform information, since this contamination can also affect us. "Ultimately, the habitat of sea turtles is much larger than that of fish - so the data reflects a regional contamination situation that is important to examine," he concludes.
More of the topic in Hayadan:
