Re: What results from combining chlorine and sodium thiophosphate

Launa,

I could not find a reference to sodium thiophosphate in the Chemical 
Rubber Handbook (the CRC).  One common dechlorinating chemical is sodium 
thiosulfate (Na2S2O3), and this may the the chemical to which you are 
referring.  Activated carbon or other chemical reducing agents such as 
sulfur dioxide, sodium sulfite, or sodium sulfite will dechlorinate.  
These reducing agents are oxidized and change active chlorine 
(hypochlorite) in water to chloride (Cl-, the anion part of table salt).  
The thiosulfite is oxidized to sulfate (SO4=).  Neither of these chemicals 
is hazardous to humans or other organisms in the concentrations typically 
found in drinking water.  Active oxidizing chlorine compounds destroy 
microorganisms by chemically *burning* their outer cell walls or cell 
membranes.  Once the active chlorine has been reduced, it is no longer a 
threat through this mechanism.  If chlorine oxidizes certain organic 
compounds such as hydrocarbon chains, however, the resulting chlorinated 
hydrocarbons (chloro-methane, chloro-ethane, etc.), can become dangerous 
as carcinogens, or cancer causing agents.  Cities along the Mississippi 
River used to unwittingly produce dangerous levels of these chlorinated 
compounds in their drinking water by incompletely treating the river 
water.  The resulting cancer rate among cities such as New Orleans, LA, 
became statistically high.  More complete reduction of these compounds 
removed this threat.

References:     Handbook of Chemistry and Physics, CRC Press, 1985.
                Betz Handbook of Industrial Water Conditioning, 1980.