When we first started chasing this down, we headed in the direction of phosphates, those eco-enemies that pollute waterways by fertilizing the algae already living there, causing massive blooms that choke out other plants and animals in the ecosystem. Phosphates are so wicked, in fact, that in 2010, 16 states banned the sale of high-phosphate detergents.
Phosphates do clean beautifully. The salt of phosphoric acid acts "like a little fatty acid that gets around food particles and makes them slippery, so they can't stick to each other, or the pan," says Daryl Thompson, a food scientist for Florida's Global Research and Discovery Group. That's how the crud on your dishes washes away easily with water. With phosphates effectively banned in automatic dishwashing detergent, manufacturers of detergents are getting besieged with complaints from consumers who say the reformulated products don't work as well.
But dishwashing liquids (soaps you squirt out of a plastic bottle to do dishes by hand, as opposed to those for the automatic dishwasher) haven't had phosphates in them for a long time—like, decades. If you did dishes in the '70s or '80s, you may have run across liquid dish soap with phosphates, and if you did, you probably noticed how effective it was.
Since phosphates have already been ruled out, what's the difference between ecofriendly and regular dish soaps? Mainly, ecofriendly soaps don't contain cleansing agents sourced from petroleum. Instead of using substances like dipropylene glycol n-butyl ether, a fine product from Dow found in the ingredient list for Dawn Power Dissolver, ecosoaps use plant-derived ingredients like lauramine oxide, derived from coconut oil and found in dish liquids from both Method and Seventh Generation.
Does the plant-based stuff work? As of yet, there have been no definitive studies comparing plant- and petroleum-based cleansers. (Interestingly, Dawn is the preferred cleanser for cleaning up birds after oil spills, which is ironic, since Dawn contains ingredients derived from the very same oil.)
Representatives from Colgate (maker of Ajax and Palmolive dish soaps) and Procter & Gamble (Dawn, Joy) also point out that some formulations are "concentrated" or "ultra-concentrated," i.e., contain higher proportions of active ingredients relative to water. You'll need less of a concentrated brand to do a sinkful of dishes, so be aware of what you're buying.
At home, Global Research and Discovery Group's Thompson doesn't even bother with store-bought dish soap—he uses a nonpolluting mix of equal parts baking soda, borax, and citric acid (use a packet of powdered lemonade mix if you can't find citric acid). Borax and baking soda are gentle abrasives, and the mixture of citric acid with water and baking soda softens the water, allowing dirt and grease to dissolve more easily. Plus, the reaction of borax with water, particularly hot water, creates hydrogen peroxide, a weak bleach.