RADIOISOTOPIC STUDY OF MERCURY UPTAKE 275 



MATERIALS AND METHODS 



Collection and Maintenance of Organisms 



Zooplankton and algae were collected from midchannel and 

 shore locations in the Hudson River 66 km north of New York City. 

 Zooplankton (see Table 2) were collected on the day preceding or on 

 the morning of an experiment with a 0.5-m-diameter nylon net 

 having a mesh size of either 76 or 500 ju. River water and algae were 

 collected by filling 4-liter plastic buckets with surface water. Algae 

 were subsequently concentrated with a nannoplankton net (18-jU 

 mesh). Gammarus sp. collected from Myriophyllum spicatum 

 gathered from the Hudson River were placed in aquariums containing 

 Hudson River water together with M. spicatum and maintained in 

 culture at ambient river temperature. 



Before use in an experiment, the larger zooplankton (Crangon, 

 Gammarus, Amnicola, Neomysis, and Chiridotea) were maintained in 

 380-liter aquariums filled with Hudson River water, and small 

 zooplankton {Eurytemora, Acartia, Daphnia, Leptodora, Cypris, 

 Mesocyclops, Monoculoides, Chaoborus nauplii and cyclopoid 

 copepodids) were kept in 800-ml battery jars filled with Hudson 

 River water. All holding vessels were placed in water troughs filled 

 with flowing river water and were illuminated on a 12 : 12 light— dark 

 cycle. Organisms were fed ad libitum before the experiment. 



Striped bass (Morone saxatilis) larvae from Hudson River stock 

 were obtained from the Consolidated Edison Hudson River fish 

 hatchery at Verplanck, N. Y. Larvae were maintained in holding 

 facilities at the hatchery before the experiment and were brought to 

 the New York University laboratory at Indian Point for acclimation 

 over a 2-day period to Hudson River water. This was accomplished 

 by serial dilution of hatchery water with Hudson River water. 

 Striped bass larvae v/ere maintained at ambient Hudson River 

 temperatures and fed brine shrimp nauplii. 



Accumulation Studies 



Organisms were taken from holding facilities and placed in 

 individual culture bowls. The numbers of organisms added to each 

 bowl varied according to species. Generally 150 to 300 microzoo- 

 plankton, 30 to 50 macrozooplankton, or 6 to 10 fish larvae were 

 placed in the experimental containers. Each bowl contained 100 ml, 

 or 300 ml in the case of fish larvae, of Hudson River water. One 

 milliliter of radioisotope carrier (~0.1 fiCi) was injected with an 



