Green Tea Increases the Concentration of Total Mercury in the Blood of Rats following an Oral Fish Tissue Bolus

Effects of cooking methods and co-ingested foods on mercury bioaccessibility in pontic shad (Alosa immaculata)

Human mercury (Hg) exposure is mostly caused by eating fish. However, there are major differences between the measured and predicted mercury concentration on Hg bioavailability. This study investigated the effects of cooking (steaming, baking, frying, marinating, and smoking) and selected components' co-ingestion on Hg bioaccessibility. Baking and frying reduced Hg bioaccessibility compared to the raw sample. The bioaccessible Hg fraction in fish was assessed through in vitro digestion method. Hg bioaccessibility varied from 4.31 to nearly 24.95% and the Hg recovery rate varied from 63.44 to 78.74%. Co-ingested garlic and broccoli with pontic shad had a positive effect on decreasing fish Hg bioaccessibility. The antioxidant activity of co-ingested food items was also calculated and correlated with mercury bioaccessibility. These results highlighted a possible positive role of plant-based foods and other food processing techniques in the bioaccessibility reduction of other chemical contaminants found in food sources.

Analysis of Mercury Content in Various Types of Tea (Camellia sinensis) and Yerba Mate (Ilex paraguariensis)

Due to the content of active ingredients, teas can be used prophylactically, but most of all they are consumed for taste reasons. As with food or water, these products can be contaminated with heavy metals, including mercury. Mercury (Hg) is a toxic element, it causes many side effects in the human body depending on the form of Hg, which can include respiratory failure, kidney damage, neurological disorders. At the cellular level, Hg and its compounds lead to a disturbance of metabolism and cell death. The aim of the study was to evaluate the mercury concentration of tea (Camellia sinensis) and Yerba Mate (Ilex paraguariensis). Eighty-six samples were collected and analyzed, including the following kinds: black, green, white, Pu-erh, and Yerba Mate. The samples came from Poland. The Hg concentration was determined with an AMA 254 atomic absorption spectrometer. The study showed that the Hg content in each tea sample averaged 2.47 μg/kg. The Hg concentration in the tested types of tea differed significantly statistically (p = 0.000). It was the largest in Yerba Mate, followed by green, Pu-erh, and white tea, and was the smallest in black tea. Statistically significant differences in the Hg content (p = 0.004) were also dependent on the form of the product; in leaf tea samples, the concentration of Hg (2.54 µg/kg) was higher than in tea bags (1.16 µg/kg). The Hg concentration determined in the tested samples does not exceed the permitted EU standard. Consuming these teas poses no health risk in terms of the amount of Hg.

Co-administration of a Rhododendron tomentosum extract does not affect mercury tissue concentrations and excretion rate in methylmercury-treated adult male rats

Objectives

Consumption of fish/seafood is clearly linked to higher mercury levels in human tissue samples. However, correlations between methylmercury (MeHg) intakes calculated from dietary surveys and mercury body burdens are usually weak and can vary across populations. Different factors may affect MeHg absorption, distribution, metabolism and excretion, including co-exposures to phytochemicals and antibiotics, which were shown to affect mercury body burdens in rodents. Based on the observation that rat pups developmentally exposed to MeHg and a Rhododendron tomentosum extract (Labrador Tea) presented significantly higher blood mercury levels at weaning compared to pups exposed to MeHg alone, the modulation of MeHg toxicokinetics by Labrador Tea was further investigated in adult rats.

Results

Total mercury levels were quantified in the blood, liver, kidney and feces of adult male rats exposed to MeHg (1.2 mg/kg bodyweight/day, for 3 weeks) administered either alone or in combination with Labrador Tea (100 mg/kg bodyweight/day) or with an antibiotics cocktail (to inhibit MeHg demethylation by gut bacteria). While the reduced fecal excretion and higher blood mercury levels expected from antibiotics-treated rats were observed, mercury levels in samples from Labrador Tea-treated rats were not significantly different from those measured in samples from rats exposed to MeHg alone.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4409-7) contains supplementary material, which is available to authorized users.

Cooking and co-ingested polyphenols reduce in vitro methylmercury bioaccessibility from fish and may alter exposure in humans

Fish consumption is a major pathway for mercury exposure in humans. Current guidelines and risk assessments assume that 100% of methylmercury (MeHg) in fish is absorbed by the human body after ingestion. However, a growing body of literature suggests that this absorption rate may be overestimated. We used an in vitro digestion method to measure MeHg bioaccessibility in commercially-purchased fish, and investigated the effects of dietary practices on MeHg bioaccessibility. Cooking had the greatest effect, decreasing bioaccessibility on average to 12.5±5.6%. Polyphenol-rich beverages also significantly reduced bioaccessibility to 22.7±3.8% and 28.6±13.9%, for green and black tea respectively. We confirmed the suspected role of polyphenols in tea as being a driver of MeHg's reduced bioaccessibility, and found that epicatechin, epigallocatechin gallate, rutin and cafeic acid could individually decrease MeHg bioaccessibility by up to 55%. When both cooking and polyphenol-rich beverage treatments were combined, only 1% of MeHg remained bioaccessible. These results call for in vivo validation, and suggest that dietary practices should be considered when setting consumer guidelines for MeHg. More realistic risk assessments could promote consumption of fish as a source of fatty acids, which can play a protective role against cardiovascular disease.