Distribution and elimination of a polychlorinated biphenyl during early life stages of rainbow trout ( Salmo gairdneri)

Abstract

Distribution and elimination of 2,5,2′,5′-tetrachlorobi[ 14C]phenyl (4-CB) were studied during the egg, sac fry, and fry stages of rainbow trout development. Fertilized eggs were exposed to water-borne [ 14C]4-CB for 24 hr and transferred to an incubator containing flowing, 4-CB-free water. The whole egg and its component parts (yolk fluid and chorionic membrane) were analyzed separately for 14C immediately after exposure ( T 0) and 1, 4, 7, 11, 14, and 21 days later. Whole sac fry and its component parts (yolk sac and larva) were analyzed on Days 26, 35, 42, and 49 and whole fry and its component parts (viscera and eviscerated body) on Days 56, 63, 77, 91, and 105. Immediately after exposure ( T 0), 4-CB content of whole eggs was 0.22 ± 0.01 μg/egg (mean ± SE) and 4-CB concentration on a whole egg wet weight basis was 3.72 ± 0.08 ppm. The majority of 4-CB in the eggs was associated with the yolk fluid where it was apparently associated with water soluble lipoproteins and oil globules composed of triglycerides. During the sac fry stage the majority of 4-CB was associated with the yolk sac. However, as the yolk sac was gradually absorbed the 4-CB was transferred to the larva. The time during sac fry development when the greatest absolute amount of 4-CB was present in the larva was at the very end of the sac fry stage. This was also the time when the oil globules in the yolk sac were first consumed by the sac fry before they began feeding on their own. The highest concentration of 4-CB in the larva occurred at the start of the sac fry stage when the eggs hatched. Thereafter larva 4-CB concentration decreased due to larval growth. The most intriguing finding had to do with a change in the rate of whole body elimination of 4-CB during the transition period from the sac fry to fry stage of development. During the egg and first two-thirds of the sac fry stage, 4-CB elimination was slow ( t 1 2 = 231 days ), but during the last one-third of the sac fry stage and throughout the fry stage it was rapid ( t 1 2 = 15 days ). This increased rate of elimination resulted in a loss of nearly all of the 4-CB from the fry. Thus, whole body 4-CB concentration dropped precipitously in the fry and this was due primarily to enhanced 4-CB elimination but also dilution by growth. The mechanism for this rapid whole body elimination of 4-CB in rainbow trout fry is not known but may be related to the low fat content of the fry body.