Mercury concentrations in the tissues of blue shark (Prionace glauca) from Sagami Bay and cephalopods from East China Sea.

The toxicity of mercury (Hg), is generally known, and around 90% of Hg exist as methylmercury (CH3Hg+) in marine organism. Mercury concentrates in sharks and whales, which are at the top of the food chain as predators to cephalopods. The concentrations of Hg in liver and muscle of blue shark, caught in Sagami Bay, and in digestive gland and mantles of Todarodes pacificus, Sepia madokai, and Uroteuthis edulis caught in East China Sea were measured and analyzed. The Hg concentrations in the sharks, squids, and cuttlefishes determined in this study were almost same as those in the other sea regions. In addition, the Hg concentration in the blue shark was higher in the muscle than in the liver. In S. madokai and U. edulis, Hg accumulated in the digestive gland but not in the mantle. Although the Hg concentration in the digestive gland of T. pacificus is lower than those of S. madkai and U edulis, Hg concentration in the mantle is critically higher. More than 90% of Hg is present as CH3Hg+ in muscle of blue shark and mantle of T. pacificus. This feature is explained due to amino acids with the thiol groups and chain genes in the muscle of blue shark as well as in the mantle of T. pacificus. Myosin in the mantle of T. pacificus and blue shark enhances the stability of CH3Hg+. The amount of Hg in the digestive gland of T. pacificus could be too large to store; thus, Hg is released to the mantle, whereas the nutrients in the digestive gland of T. pacificus are supplied to other tissues. It is considered that the muscle fiber of T. pacificus is strong; therefore, large amounts of myosin levels may be present in T. pacificus than in S. madokai and U. edulis.

As, Cd and Hg in the organs of Todarodes pacificus, Sepia longipes and Sepia madokai in the East China Sea.

Arsenic and Cadmium concentrations in Todarodes pacificus (4 males and 4 females), Sepia longipes (1 male and 3 unknown), five Sepia madokai caught in 2012 (1 male and 4 females) and five S. madokai caught in 2014 (5 females) were collected from the East China Sea (ECS) during intervals from 2010 Oct. through to 2014 Oct. The internal organs were vacuum dried and the elements were measured by ICP-MS. Among the toxic elements, As, Cd, and Hg in the digestive gland, gonads and branchial hearts of squids and cuttlefishes were measured separately. The squid T. pacificus practically inhabits offshore, whereas cuttlefishes, such as S. longipes and S. madokai, inhabit bottom coastal waters in the ECS. Cd concentration in digestive gland of T. pacificus and S. madokai is higher than similar species from other regions. This high concentration seems to be derived from anthropogenic activities and geological conditions present in the ECS. The squid and cuttlefish also accumulate high amounts of As, not only in their digestive gland but also in other organs. Arsenic could be derived from high volcanic activities. In the case of Hg, the muscles were reported to contain the highest concentration in the species studied, but unlike concentration of Cd in digestive gland, it was high compared to other studies. These elements can be utilized as indicators for environmental pollution in marine systems. For monitoring of harmful elements in squids and cuttlefish, for example Cd and As in the digestive gland and Hg in mantle should be measured.