Hazards of consumer products to the water cycle

‘The research into consumer products is an initial study, in which we point to the knowledge that is still lacking,’ says Gerlinde Roskam, researcher at Deltares. ‘For instance, 80 percent of the substances that were investigated do not have a registry number, which is something we need in order to collect information about them.’ A follow-up study, which will involve further research on a number of substances, should provide water managers with a better understanding of the scale of the problem.

Reducing emissions

The Deltafact Consumer Products is a product of the Water Quality Knowledge Impulse (KIWK) programme. The programme recently also published the Deltafact Microplastics, and the Deltafact Biocides (both in Dutch). The objective of the chain explorer is to chart various aspects of a selected number of substance groups, with the ultimate aim of reducing their emissions into the aquatic environment.

Difficult group of substances

According to KWR researcher Thomas ter Laak, consumer products – including shampoo, dishwasher detergent, toothpaste and deodorant – present a major conceptual challenge. ‘Chemically speaking, they are not a substance group, because they contain chemicals with widely diverse structures and properties. Consumer products are for the most part still uncharted territory.’ Moreover, the substances are not all subject to the same legislation.’ In 2019, on a commission from Rijkswaterstaat Water, Traffic and Environment Service (RWS WVL), and at the initiative of the Emerging Substances Working Group, Deltares conducted a study on substances present in consumer products. The Deltafact Consumer Products builds upon this previous work. The first task was to determine which consumer products to investigate. A choice was made of those consumer products that (principally) via the sewer system and wastewater treatment end up in surface water, where they can possibly have a damaging impact on the ecosystem. Roskam: ‘“Wash-off” is a term from the world of personal care products, and refers to products that do not stay on the skin or hair, but are washed off. To this category we added “wash” products, such as cleaning products and (dishwasher) detergents.’

Twenty product groups

The starting point for the previous 2019 study was the American CPDAT (Chemical and Products Database), with ingredients from all kinds of products, from which Roskam selected twenty product groups, like shampoo, toothpaste and dishwashing detergent. A compilation of 6054 individual products was then made. Information was also collected from various sources about the use of these products by consumers.

Registry number lacking

The researchers quickly ran into a big roadblock. ‘Eighty percent of the total of 6384 different substances had no Chemical Abstract Services Registry Number,’ says Roskam. Without this CAS number it is impossible for instance to automatically find out about the substance properties, which renders further testing difficult. ‘This makes the information incomplete.’

Dealing with assumptions

There is yet another relevant factor regarding the knowledge gaps about consumer products and their impact on water quality, explains Roskam. ‘After I had trimmed the list of substances to come up with one with CAS numbers, I still had to deal with a lot of assumptions. How often is the product used? How effectively are the substances it contains removed in treatment? What concentrations of the substances end up in the water system? What does this say about the anticipated hazards? There are moreover substances that are also used in other products, which means you can’t attribute them all to consumer products. Also, most of the substances are not yet monitored in water. So we don’t in fact know whether they are present in the water system.’

Follow-up study for prioritisation

What this Deltafact makes clear, is that we are still far from the possibility of answering the question as to which substances, and consequently which consumer products, present a problem to water quality in our country. To achieve this, we need much more information about consumption volumes, substance properties and effects. Roskam: ‘There is still so much knowledge missing, that the uncertainties are too great to permit any statements about possible hazards. Ter Laak adds: ‘For water managers this means that they realise that consumer products are a difficult group of substances. This is the reason why we will, in a follow-up study, investigate a number of substances more closely, by getting a clearer picture of the estimated environmental concentrations and the toxicology. By comparing the results of the different substances, we will be able to prioritise them on the basis of expert judgement. The prioritisation will indicate which substance groups within the consumer products we consider to be more or less hazardous to the environment. This will make the subject less elusive and allow water managers to better incorporate the matter into their decision-making.’