On July 28th, 2022, Dr. Mi-Ling Li presented virtually on Pollution in the Ocean as part of the university’s Ocean Currents Lecture Series. Dr. Mi-Ling Li teaches in the School of Marine Science and Policy and the department of Earth Sciences, Water Sciences and Policy. She is an Assistant Professor of Environmental Chemistry and Toxicology.

Dr. Mi-Ling Li is studying ocean pollution in Delaware and is working with the Delaware Sea Grant to take samples around the Delaware Bay. 

Dr. Li spoke about inorganic and organic pollutants of the ocean. She focused on mercury when discussing inorganic pollutants and poly or perfluoroalkyl substances (PFAs) when discussing organic pollutants.

Heavy metals are a natural part of the Earth’s crust, consequently entering the sea. Some of these metals are biological essentials like copper, iron and zinc, and some of them are nonbiological essentials like lead, mercury and cadmium. Mercury is a chemical pollutant of the ocean that is unique in its ability to remain a liquid at room temperature. The coal surge and artisanal industry have greatly increased mercury emissions. Many commercial products contain mercury. The elemental form of mercury, Hg(0), is volatile, but MeHg (methyl mercury) is poisonous and Hg 2+ is toxic. Hg 2+ is becoming increasily prevalent in the oceans and is easily taken up by phytoplankton. Phytoplankton is the basis of many oceanic food chains. As one goes farther up the food chain, mercury concentration increases. This means that predators like humans are the organisms that face the greatest threat from mercury consumption. 

Methyl mercury is a powerful neurotoxicant that is able to pass the human blood brain barrier because it looks nearly identical to the essential amino acid cysteine. Fetal exposure to mercury can hinder neurological development, resulting to IQ deficits and other neurological deficiencies. Adult exposure can result in hypertension and arteriosclerosis of the carotid arteries. 

Most of the mercury that humans consume comes from seafood. Groups such as islanders that live near oceans have seafood heavy diets, experiencing the most health issues from mercury. Of the seafood in the American diet, tuna is responsible for the majority of methyl mercury consumed. 

Eliminating seafood from the human diet is not an ideal or practical solution to mercury consumption, as fish have many nutrients–like omega 3– that are crucial to human health. While it is best to avoid tuna, other fish like salmon are perfectly safe to consume. 

Read the fda guidelines for having a safe seafood diet here: https://www.fda.gov/food/consumers/advice-about-eating-fish

Global regulations on mercury emissions are necessary in order to minimize the negative effects of mercury on ecosystems. 265 nations have signed a global mercury treaty. 

Next to mercury, poly and perfluoroalkyl substances (PFA) are some of the most dangerous ocean pollutions. PFA is an organic pollutant, made up of an alkyl chain with hydrogen atoms that are partially or fully replaced by fluorine atoms. PFAs are bioaccumulative, meaning that they develop in greater concentrations in the tissues of organisms than the environment they inhabit.

PFA is a manmade pollutant, created by Dupont in the 1940s. It is used for many purposes, such as repelling water and stains, food packaging, cookware and household items. PFAs are extremely dangerous, having a wide range of health effects. PFAs can transfer to infants through breast milk and cord blood. PFAs can, for example, cause thyroid disease, increase cholesterol and make vaccines less effective. 95% of adults and adolescents in the United States have measurable levels of four different types of PFAs. There are no existing national regulations on PFAs, making it difficult to limit human exposure. The USEPA previously advised 70 ppt (parts per trillion) of PPAs as the maximum safe amount of PPAs in a product, but in June gave an interim advisory of .004 ppt of PFOA and .02 ppt of PFOS, the two most common types of PFAs. 

Minimal studies have been done on PFAs in Delaware, which is why researchers like Dr. Mi-Ling Li are working to study Delaware’s water. Existing data shows massive amounts of PFAs in Delaware’s water, with Artesian water company having levels of around 1,940 ppt and Blades drinking water having levels of around 187 ppt. With more data on Delaware’s water quality, effective action can be taken to limit the amount of pollutants in the oceans.