group using the same animals and techniques similar to those used 

 in petroleum experiments. Chlorine ion regulation was studied as a 

 physiological indicator of mercury pollution. Although ninety-six 

 hour LC50 values ranged from 50 to 64 part per billion of mercury for 

 the porcelain crab {Petrolisthes armatus) this exposure did not alter 

 chlorine ion regulation (Roesijadi et al., 1974). Likewise blood chlo- 

 ride ion regulation of the grass shrimp {Palaemonetes pugio) was un- 

 affected by exposure of the animals to 50 ppb of cadmium. 



During a cruise in the Gulf of Mexico aboard Texas A&M's R/V 

 Gyre penaeid shrimp, Penaeus aztecus, were collected and tested for 

 accumulation of mercury (Hg) and the effects of Hg exposure on 

 chloride ion regulation. Control animals contained 4.6 ppb Hg, which 

 was distributed as 64% in the "meats" and 36% in the "shell" or 

 exoskeleton. After exposure to 500 ppb Hg for 2 hours, shrimp con- 

 tained a mean level of 285 ppb of which 91 % was associated with the 

 exoskeleton. While this short-term exposure to a high level of Hg re- 

 sulted in most of the metal being absorbed to the exoskeleton, long- 

 term low level exposures produce higher concentrations in the internal 

 organs and tissues. Shrimp exposed to 500 ppb and transferred from 

 environmental salinity (28%o) to 14%^ were less able to adjust internal 

 chloride ion concentrations than control animals. 



Studies with mercury and postlarvae of the white shrimp, Penaeus 

 setiferus, were also conducted at Texas A&M. Toxicity studies with 

 Hg showed that two different size classes (7-13 mm and 15-25 mm) 

 exhibited approximately the same 96 hour LC50 value (17-20 ppb). 

 Even after a 60 day period of pre-exposure to 1 ppb, the 96 hour LCgo 

 remained essentially unchanged. Other measurements taken after the 

 60 day period of exposure to either 0.5 or 1.0 ppb of Hg failed to 

 demonstrate any sublethal effect of these long-term exposures. Res- 

 piratory rate of postlarvae, as well as growth and molting rate were 

 not significantly affected by 60 days exposure to either 0.5 or 1.0 ppb 

 of Hg. It is again interesting to note that no sublethal effects are ex- 

 hibited at 1 ppb, while the 96 hour LC-,o value for these postlarvae is 

 a little over one order of magnitude higher ( 1 7-20 ppb Hg) . 



Polychlorinated Biphenyls (PCBs) 



The Texas A&M group studied the biological effects of PCRs mak- 

 ing use of procedures developed in petroleum and trace metal work. 

 Chemical analyses of the exposure media were conducted during these 

 experiments and it was found that concentrations of Aroclor 1254 in 

 exposure media decreased with time, dropping to 20% of initial values 



37 



