The total arsenic in seafood samples consumed in the USA varied greatly in the range of 8-22200 ng/g (wet mass). However the most toxic inorganic arsenic species (iAs) was found only in clams and crabs, while non-toxic arsenobetaine (AsB) predominates in most samples.
Human exposure to arsenic results mainly from contaminated drinking water and seafood. Arsenic is one of the metal(oid) of concern who's toxicity depends
heavily on its chemical form. Inorganic arsenic (iAs) is a known
carcinogen that has also been associated with several additional health
problems including heart disease and diabetes. A valuable risk
assessment therefore has to based on the arsenic species being present
rather than on the total arsenic concentration.
Photo: seafood plate (CC BY-SA 3.0,
The new study:
researchers collected fifty-four seafood samples from local
supermarkets and their genospecies was identified by DNA barcoding. The
study focused on the determination of arsenic species in the top ten
most consumed seafoods in the US. Over the last 9 years, shrimp is the
leasing product followed by salmon and canned tuna, altogether
representing more than 50% of total consumption. The other products in
the list are tilapia, pollock, pangasius (swai), cod, crab, catfish, and
clams. The samples were analyzed for total arsenic, water-soluble
arsenic species, and total nonpolar arsenic fraction using a method
developed and validated by the FDA. The speciation analysis is based on
anion and cation HPLC coupled to inductively coupled plasma mass
The concentration of total arsenic in the different seafood samples varied greatly between 8 and 22200 ng/g, with highest levels in crab and lowest in swai and catfish.
Water soluble arsenic fraction
The water soluble arsenic fraction varied from 8-112 %. Arsenic was nearly quantitatively extracted with water from all the tilapia, pollock, and cod samples. Also for most of the shrimp, tuna and crab samples the majority of arsenic was water soluble.
Water soluble arsenic species
Analyte species separated by HPLC were identified by matching their retention times with those of standards. A total of 16 known and 12 unknown arsenic species were detected. Crab and clam samples had the greatest diversity of arsenic species.
Regardless of the very different total arsenic concentration in different seafood samples, inorganic As was either not detectable or present at very low concentration. The highest level found was 145 ng/g in a golden king crab sample.
Arsenobetaine, a nontoxic arsenic species, represented the highest fraction of total arsenic in most of the samples.
Arsenosugars were major components in most of the crabs and clams. None of the finfish and shrimp samples contained any arsenosugar.
Other water-soluble arsenicals
Trimethylarsoniopropionate (TMAP) was found in most matrices with elevated concentrations in crabs (130-800 ng/g). Tetramethylarsonium (TMA) was detected at relatively higher concentrations of 25-90 ng/g in a few samples (shrimp, cod, and crab). Methylarsonic acid (MMA) and trimethylarsine oxide (TMAO) were found almost exclusively in crabs.
Nonpolar arsenic species represented 1-46% of the total arsenic in the respective samples. On average, highest nonpolar fractions were found in catfish (31%) and salmon (26%).
The researchers concluded, that the concentrations of the toxic inorganic arsenic in America’s most consumed seafood products are much lower than the tolerable intake set by the Joint FAO/WHO Expert Committee, even at the highest levels found in this study.
While without doubt, this study represents the most comprehensive survey both in terms of the most relevant seafoods for U.S. consumers and the number of arsenic species evaluated, it also has its limitations. The authors have to admit, that low extraction efficiency and poor chromatographic recovery presented major obstacles to a more complete understanding of arsenic species in certain matrices. Arsenocholine (AsC), dimethylarsinic acid (DMA), dimethylarsinoylacetic acid (DMAA), and dimethylarsinoyl ethanol (DMAE) were present at trace levels throughout
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