The question we get asked most often is “are your bags biodegradable?”. You would think there would be a simple answer to this question, but the answer is more complicated than most people imagine. For example, the location where something degrades can determine how quickly the process takes, and what it degrades into.
The reality is that the vast majority of dog poo bags end up in landfill, and in offering a product, we believe our responsibility extends beyond the point of our bags being placed in a rubbish bin. This is where things become complicated. Because when you send biological material to the landfill, it can be very bad for the Planet. So here's an explanation as to why we use HDPE (high density polyethylene) bags rather than cornstarch.
In an ideal world, everyone would have a compost heap in their back yard. Unfortunately, there are reasons why most people don’t attempt to compost dog poo. And it’s not necessarily a lack of space or the ick factor. Dog poo contains pathogens and if not handled properly can spread nasty diseases around the neighbourhood. In order to kill these pathogens, a temperature of 60 degrees Celsius needs to be achieved and maintained. This means your compost heap requires constant attention. If you presently use cornstarch bags for dog poo pick up and they are not breaking down quickly in your compost heap, it's probably an indication that optimum temperature is not being maintained, because cornstarch ideally requires prolonged temperatures of 60 degrees in order to breakdown quickly. If not commercially composted, a cornstarch bag actually takes a long time to break down in the urban environment, and even longer in seawater.
So, why do we use HDPE rather than cornstarch. The answer is that if you landfill a cornstarch bag, it will eventually break down. Unfortunately that is not as good as it sounds because, due to the absence of oxygen in landfill, the bag and its contents will degrade anaerobically. This produces methane, which is serious Greenhouse Gas. It has an atmospheric heating capacity 30 times that of CO2. So, landfilling a poo in a cornstarch bag increases its potential effect on Global Warming by 3,000%. Using an HDPE bag (which is impervious to water, essential for the degradation process) sequesters the carbon contents of the poo, taking it out of the carbon cycle. The easiest way to think of it is reverse coal mining.
Landfilling is an emotive issue, but for the foreseeable future, some of our waste will continue to be buried. However, the first thing we should be removing from our landfill waste stream is biodegradable material because, if it degrades there, all of its carbon content can be converted to methane. Some landfills capture methane and use it to power turbines to produce electricity. Unfortunately, methane is lighter than air and landfills have no lid, so it’s impossible to capture all the methane. Take 100 tons of methane. If just 10% of it is lost to the atmosphere, this is the equivalent of 300 tons of CO2e. Unfortunately, the average gas capture rate for landfills in New Zealand is 64%. So the problem is huge. Globally, landfills account for around 11% of anthropogenic (human produced) methane.
If you are interested, here’s a quick way to calculate your dog’s potential carbon footprint. The average dog produces around 100g of poop per day. That’s 36.5kg per year. If all that turns to methane, multiplied by 30, that’s just over one metric ton of CO2e per year. Of course, depending on their size, some dogs produce more methane than others.
If you would like to offset your pet’s carbon footprint, we recommend you hire a green waste bin which is collected by a commercial composter. You can save up to 4 tonnes CO2e per household per year by diverting all your green waste and kitchen scraps to commercial composters. Unfortunately, one of the things they won’t presently accept is dog poo. So, in the meantime, if you don’t have a home compost bin, we recommend you continue to use HDPE bags.