The method for analizing vitamin B
12 binder in natural seawater was evaluated. Based on this evaluation, the distribution and seasonal variation of free and bound B
12 in the water of Uranouchi Inlet were investigated. Through these studies, the relationship between the content of B
12 compounds and other environmental factors in seawater is discussed.
The protein-coated charcoal method was found to be an applicable and reliable why to determine the B
12 binder in seawater samples. The water of Uranouchi Inlet is rather eutrophied, and the content of total B
12 in the water ranged from 1.5 to 15.2ng/
l. The concentration of free B
12 was 0.02-12.9ng/
l. The content of B
12 bound to B
12 binder (bound B
12) ranger from 0 to 5.1ng/
l in the water. The ratio of bound B
12 to total B
12 averaged 35%. The content of bound B
12 correlated closely with the concentration of chlorophyll
a, phosphorus, and COD, therefore some of the sources of B
12 binder in seawater seem to be produced by phytoplankton and/or organic substances.
The result reveals that the B
12 binder exists in eutrophic seawaters to some extent all year round, and that the B
12 binder in the water could influence the growth of organisms requiring B
12 and the succession of phytoplankton species.
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