Table 1. Continued 



Chemical System Type 



Methoxychlor, DDT, fonofos, aldrin Terrestrial monoculture (T) 



Dieldrin phorate, HCB, PCNB, PCP, captan, Physical model ecosystem 



2,4,5-T, simazine, trifluralin, methyl parathion,{T-FW) 



parathion 



Dieldrin, methyl parathion, parathion, Terrestrial microcosm 



p-nitrophenol, HCB, PCP, PCNB, 2,4,5-T, chamber (T) 



captan, simazine, bromacil, trifluralin 



Dieldrin, bis-tributyltin oxide, PCP, creosote TMC (T) 



( phenanthrene, acenaphthene) 



TABLE 2. CHEMICALS STUDIED IN EXCISED MODEL SYSTEMS^ 



Chemical System Type 



Dieldrin, 2,4,5-T, methyl parathion, HCB 5 X 10 cm soil core 



Sodium arsenate, HCB 5X10 soil core 



Methyl parathion, carbaryl, PCP, dimilin Eco-core (Estuarine) 



Pb, Cd, Zn, Cu Large soil core 



DDT, Cd, toxaphene, Aroclor 1242 Freshwater pond 



PCBs, DDT, and related compounds, HCB Freshwater Pond 

 Clorpyrifos, dieldrin 



2,4-D, CIPC, monuron, atrazine Freshwater pond 



HCB, bis-(ethylhexyl)phthalate Benthic bucket 



studies, but the latter contains only soil and plants. Both the TMC and the Metcalf 

 terrestrial systems contain a Microtus species of field mouse as the highest terrestrial 

 consumer. 



These new systems permit temporal and spatial analysis of chemical fate. 

 However, the biological facets of toxicity are still simply "flagged" by observations of 

 an anecdotal nature. It is hard to obtain statistics on a single vole in a system. 

 Moreover, the vole causes considerable destruction, digging up the soil and 

 consuming all or most of the other biota. The animals leave "elephant tracks" 

 through the system. In spite of these difficulties, the systems behave consistently 

 upon limited replication and generally agree with available data on chemicals in the 

 field. Clearly these microcosms are better for providing chemical fate data than 

 ecotoxicological information. 



During the last part of the 1 970s the pressures of impending legislation regarding 

 toxic substances and for a more incisive approach to evaluation of pesticides and 

 hazardous wastes began to be felt by both regulatory agencies and the chemical 

 industry alike. The techniques useful for studying pesticides and drugs were too 

 resource-intensive and sophisticated to be applied across the board to a hundred 

 times as many chemicals. Laboratory model ecosystems or microcosms offered what 



156 



