The dirty truth about phosphates in detergent

New Zealand’s number one green priority is often said to be improving the quality of our lakes and rivers. When the Parliamentary Commissioner for the Environment, Dr Jan Wright, researched the issue she found pathogens, sediment and nutrients were the main things ruining our waterways. Too many nutrients in water – known as eutrophication – encourages the excessive growth of large aquatic plants such as lakeweed, slimy films (think didymo or rock snot) and phytoplankton. Especially in summer, phytoplankton (or algal) blooms can discolour water and produce toxins that make water undrinkable. And when the plants eventually die, they decompose on the bottom releasing unpleasant odours and depleting oxygen in the water.

The villains

The nutrients of concern are phosphates and nitrogen-containing compounds (urea, ammonia, and nitrates). Phosphorous and nitrogen are both essential plant nutrients and therefore applied as fertiliser to farms, so agriculture, particularly intensive dairy farming, is the main source of unwanted nutrients in fresh water. But farming’s not the whole story…

Down your drain

Households put less phosphate into our waterways than farms, but they still contribute. Phosphorous is one of the basic components of life: phosphodiester bonds hold our DNA together, adenosine triphosphate (ATP) is the main energy currency of all cells and our bones are a blend of calcium and phosphate. So phosphate is present in all living creatures – and present in human sewage, which ends up in our water in some form.

Phosphates are also a significant component of household cleaners where they help dissolve dirt, and bind up other compounds (such as calcium in hard water) which reduce the effectiveness of detergents. Household cleaners have been adding unwanted phosphate to waste water systems since the 1960s.

The good news

Unlike many environmental stories, this one is not all bad news. The problem has been recognised and in the last three or four years manufacturers have moved to greatly reduce the amount of phosphate in household cleaners. Whereas phosphate once abounded in laundry powders, now most bear labels saying "phosphate free” or “NP” (no phosphate). That said, when you read the fine print, there may still be up to 0.5 per cent phosphate present.

Some stainless steel cleaners contain about five per cent phosphoric acid but generally these cleaners are only used in small amounts.

One area where there may still be a problem is in dishwashing powders and detergents. For instance, Finish Powerball contains more than 30 per cent phosphate, although Cussons Morning Fresh super concentrated dishwasher tablets claims to be phosphate-free.

Do the ‘green’ products work?

Given their downsides, why do some manufacturers retain phosphates? Basically, because removing phosphates from dishwashing detergents seems to considerably reduce their effectiveness, although possibly more expensive ingredients could substitute. In the USA, legislation compelled the removal of phosphates from dishwashing detergents in July 2010, and so severe was the reduction in cleaning power some people purchased new dishwashers, thinking their old ones were broken! Others reportedly bought phosphates to add back to failing dishwashing detergents.

Fighting back

So are household phosphate discharges still a problem? Despite recent gains, the short answer is ‘yes’. A recent survey of the 270 households in the Lake Okareka community of Rotorua by the Rotorua District Council (RDC) estimated their dishwashers and washing machines are still flushing 142kg of phosphate a year. To put this in perspective, one kilogram of phosphate can result in the growth of up to 700kg of unwanted aquatic algae!

Councils at present treat waste water to reduce phosphate but this costs money and removal is incomplete. For instance, Palmerston North spends about $500,000 each year removing phosphate (using aluminium sulphate), so there is a real taxpayer burden in those clean dishes.

Meanwhile in Rotorua biological treatments remove about half of the phosphorus in waste water and the treated water is sprayed into pine forest. Rotorua claims to have seen a decline in phosphate levels of incoming raw waste water from 8.5mg/l to 5.5mg/l over the last few years as phosphate has been removed from laundry detergents. Alison Lowe, a senior environmental scientist with RDC, told me, “We thought perhaps 30 per cent of phosphate in our waste water was still coming from cleaners, but since the Lake Okareka study, which included distributing phosphate-free dishwasher tablets to households, we have lowered that [estimate] to 10 per cent.”

The rest comes from human waste, wastemasters in sinks, groundwater leakage into waste water pipes and industry.

Do your bit

Switching to phosphate-free cleaners will make a modest improvement to the quality of your waste water. If your town’s treated waste water is discharged into a lake or slow-flowing river, it’s a change worth considering.

Where discharge is into the sea (eg. Wellington, North Shore), it’s not going to matter much. And if you have a septic tank, do nothing: the phosphate will fertilise your lawn or trees.

So how do you know what you’re buying? Mostly you can’t as labels are poor, but read them carefully – even the bottom of the box.

A few list ingredients with percentages, others give an active ingredient or two. Some say NP (no phosphate), whereas several just claim they are biodegradable. So is cyanide! Biodegradable does not mean phosphate-free! If in doubt phone the manufacturer. I’d recommend using well-labelled products and washing dishes by hand.

A greener clean

Eco brands have led the move away from phosphate in laundry and dishwash products (the best are also free of ammonia, nitrates and chlorine) and now mainstream companies are following.

All of the below are phosphate-free. If you’re unsure about your favourite product, check for an “NP” (no phosphate) label.

ecostore Auto Dish Powder
$10.95 for 1kg

Earthwise Dish Wash Liquid Concentrate
$3.99 for 500ml

Surf Tropical Oasis laundry powder
$8.69 for 1kg

Persil Active Clean laundry powder
$8.69 for 1kg