I was looking at various detergents yesterday, Wisk, All, Dawn, Cascade, and I noticed that every one of them mentioned something about Phosphates. They all said ‘no phosphates’ except for Cascade (dish washer detergent) which said it had something like 6.2 grams of phosphorus in this form…
What’s the big deal with phosphates? Why would you want them in your soap, and why wouldn’t you want them in your soap?
Phosphate was originally put in laundry detergents because it’s a good cleaning agent. Its salts and complexes tend to be soluble, which allows it to lift dirt and stains from fabrics.
Unfortunately, phosphate is also the limiting nutrient in most lakes and streams, and adding it to these waters, via waste treatment plants, results in massive algal blooms. This eutrophication can result in slimy green lakes and rivers, with oxygen levels so low that all the fish die. This is undesirable, so, back in the 70’s, many states passed laws to limit the phosphate concentration of detergents.
Phosphorus is one of the rarest elements necessary for life. (I’m not sure where it stands vis-à-vis cobalt, but you get the picture.) That’s not to say it’s particularly rare, just that it’s not available in massive quantities virtually everywhere you look, as calcium or carbon or sulfur seemingly are.
Phosphates are an ingredient in most fertilizers; quantities of it in drainwater lead to two negative effects, one on the ecology at present and one a long-range disaster scenario that is quite real if not imminent. First, excess phosphate in the drainwater tends to lead to the eutrophication of any bodies of water it’s expelled into (even after wastewater processing; it’s apparently difficult to extract from water it’s dissolved in) and hence burgeoning growth of aquatic vegetation that may not be desired, with accompanying siltation and potentially the eventual filling in of the water body. Second, because it’s relatively scarce, and easily soluble, the eventual result of “running phosphates down the drain” is that they will accumulate in the inaccessible ocean basins (which have only been visited once, in 1960… just to get that out of people’s systems ;)), leading to a relative phosphorus shortage and consequent decline in soil fertility. As noted, this is a long-range effect, but one that can happen if steps are not taken to ameliorate it.
I’m not totally clear what phosphate does or doesn’t do in detergents, though it’s instructive to note that Cascade advertizing tends to note that it leaves glasses “sparkling clean” while other products that used to do similar promotional messages have switched to other advantages for their product.
(Note: “phosphate” in the singular is the phosphate ion -PO[sub]3[/sub][sup]+2[/sup]. “Phosphates” in the plural references the various compounds containing that ion and present in nature or in manmade products. Guano, for example, is rich in calcium, potassium, and magnesium phosphates.)
Squink has the correct answer. Cite
Why would they outlaw the use in laundry but not in automatic dishwashers?
Dishwashers weren’t all that common back then, plus phosphates have have any number of niche uses, such as trisodium polyphosphate (tsp) for cleaning walls, that they didn’t want to eliminate. Dishwasher detergents likely fell through that crack.
Phosphates (e.g. sodium tripolyphosphate, Na[sub]5[/sub]P[sub]3[/sub]O[sub]10[/sub]) were originally added to detergents to lessen the effect of hard water. ‘Hard’ water is high in calcium and magnesium ions, and these ions interfere with some detergents (such as ordinary soap made from fat and a base). Sodium tripolyphosphate sequesters the calcium and magnesium ions in hard water, preventing them from interfering with the detergent. Since phosphates cause eutrophication, they’ve mostly been superseded with other water-softening agents and with detergents that aren’t as susceptible to water hardness. I’m not sure why dishwasher detergents still contain phosphate – it might be because the detergents used for dishwashing are susceptible to hard water and phosphates are the only suitable softening agent. (The fact that dishwashers use very hot water, hotter than any other domestic washing appliance, might also be significant.)
Polycarp: It’s not so much that phosphorus is exceedingly rare as that organisms need an awful lot of it for something that’s not very common. AFAIK there’s a lot more phosphorus in the environment than there is cobalt (or molybdenum, for that matter). It’s just that an organism needs a very small amount of those; for a single-celled organism, it may be on the order of tens or hundreds of atoms.
I’m going to do a note like yours, because these are often mixed up: Phosphorus is the element P; phosphorous acid is a substance, H[sub]3[/sub]PO[sub]3[/sub], derived from the phosphite ion, PO[sub]3[/sub][sup]3-[/sup], containing P(III) (phosphorus with three missing electrons). The word ‘phosphorous’ is used in chemistry only to refer to compounds containing P(III), and never to refer to P itself.
The trouble with phosphates was with overall pollution control in the sixties which came to a head in the seventies. Rubbish was dumped to landfills. Most liquid waste was simply dumped into holding tanks to remove the harmful stuff then dumped into rivers. The new formulations of phosphates made washing in hard water easier but this new waste water remained sudsy way past the cycle where it was returned to nature. We had to rethink what was deemed harmful to the environment - phosphates were not inherently poisonous like arsenic or lead, so was allowed to run through the system.
[By the way, some places that are phosphate poor actually benefitted by the release of phosphates. 
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