Contaminant pathways in Port Curtis: Final report - OzCoasts

Contaminant pathways in Port Curtis: Final report8: Effect of pulse eventsIn general, intracellular copper increased very slowly in the initial 20 h, and thenbegan to accumulate in cells as exposure time increased (Figure 8.3). Oncecopper internalisation commenced, the intracellular copper uptake was stillrelatively linear over the duration of the bioassay for the 10, 30, and 50 µg/Lcopper bioassays with rates of 29, 66, and 74 ng/×10 8 cells/h, respectively(Figure 8.3). Higher exposure concentrations and longer exposure times resultedin greater intracellular concentrations.These results indicated that the internalisation of copper occurs more slowly thancopper binding at the cell surface (extracellular copper) and may be a rate-limitingstep for toxic effects. This is in agreement with other studies (Knauer et al. 1997;Hassler et al. 2004; Slaveykova & Wilkinson 2002). Furthermore, the rate ofcopper internalisation did not increase linearly with increasing copperconcentration in the external exposure solution. These observations haveimportant implications for how pulse copper exposures may cause toxic effects.For short-duration copper pulses, there may be insufficient time for the toxiceffects to occur before the external exposure is removed.8.3.4 Copper eliminationTo investigate potential copper elimination by cells and algal growth recoveryfollowing exposure to 10 µg Cu /L for 72 h, the exposure solution was removedand the algal cells resuspended in clean sea water containing nutrients. Whenalgal cells were placed in clean sea water, the extracellular and intracellularcopper decreased with time and was below detection after 27 h (Figure 8.4A, B).The results indicated that the elimination of extracellular copper from the cellsoccurs through both desorption and dilution following cell division, while theelimination of intracellular copper from the cells was due to dilution via celldivision, rather than due to efflux of copper from the cell.Possible mechanisms for the elimination of copper from the algae cells include(i) desorption of extracellular copper into clean sea water, (ii) efflux of intracellularcopper from cells, and (iii) dilution of extracellular and intracellular copper throughcell division and growth of the algae in the clean sea water. During the desorptionperiod, the intracellular copper concentration remained reasonably constant for theinitial 6 h, indicating negligible efflux of intracellular copper occurred during the thisperiod (Figure 8.4B). The intracellular copper concentration began to decreaserapidly 6 h after the desorption experiments commenced and coincided with theincrease in cell division. P. tricornutum are also capable of incorporatingintracellular copper into inert bodies such as vacuoles or binding copper withphytochelatins to reduce toxicity (Knauer et al. 1997).104