where cpm(เหงือก) is the total Cd counts in the gills gills. The internal organs in the carcass were included in the uptake calculation, since some of the Cd retained in these organs during the 24-h exposure has to be taken up from the water into the gill epithelium before influx to the circulatory system and internal organs occurs. The inclusion of carcass Cd in the uptake calculation may have caused a slight overestimation of the apical uptake in the gills, since some of the Cd in the carcass may have originated from the skin. The amount of Cd in the carcass after a 24-h Cd exposure is, however, low in comparison to the amount retained in the gills, so the small contribution of ‘skin Cd’ will not markedly affect the calculation of apical Cd uptake in the gills. The gastrointestinal tract, head, skin and fins were not included in this calculation, since these tissues contain a large fraction of Cd that has been taken up directly from the water, without passing the gills. The small amount of Cd detected in the gastrointestinal tract mainly originates from ingestion of water by the fish. The head, skin and fins of zebrafish contain a large fraction of Cd that has been taken up directly from the water into the surface epithelium without further passage to the circulatory system