You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Metal bioavailability from different natural prey to a marine predator Nassarius siquijorensis. Gastropods are often the top predators in marine benthic environments, and trophic transfer is the predominant route by which metals are accumulated in these predators. In the present study, the potential influences of prey composition on the trophic transfer, accumulation, subcellular distribution and metallothionein induction of six metals (Ag, As, Cd, Cu, Pb and Zn) in a predator Nassarius siquijorensis were investigated. The snails were fed venerid clams Ruditapes philippinarum, mussels Perna viridis, oysters Crassostrea angulata or barnacles Fistulobalanus albicostatus, each differing greatly in their metal accumulation and handling patterns. N. siquijorensis showed prey-specific bioaccumulation and trophic transfer of the six metals. In general, the body burdens of metals in the viscera and muscles of N. siquijorensis increased with increasing exposure period and metal concentration in the four prey. The calculated trophic transfer factors (TTFs) of the metals in different prey varied and were the highest for clams and mussels prey, indicating that metal bioavailability from these prey was higher than that from barnacles and oysters. All the studied metals except Pb were enriched during transfer to the snails. The subcellular metal distribution in the viscera was affected by prey composition. Exposure to the four natural prey induced MTs, which may be used as a better biomarker for muscle than for viscera for metal stress. Our results imply that metals from different natural prey have different bioavailability and may help better understand the trophic transfer of metals in marine benthic food chain.
{"Chemical": ["Pb", "As", "Zn", "Ag", "Cd", "Cu"]}