Environmental risk assessment of phosphonates, used in domestic laundry and cleaning agents in the Netherlands

Abstract

In the long-term cooperative project Voluntary Plan of Action (1990) between the Dutch Soap and Detergent Association (NVZ) and the Dutch Ministry of Housing, Spatial Planning and the Environment (VROM) environmental risk assessments of several main components of laundry cleaning formulations were completed. As a part of that project the environmental risk assessment of HEDP, ATMP, EDTMP and DTPMP phosphonates used in detergent applications has been carried out according to the EU Technical Guidance Document for Environmental Risk Assessment for New and Existing Chemicals. All PEC/PNEC ratios were well below 1. Results of this assessment based on the total industry volumes from 1995 and 1998 indicate that the environmental risk of these phosphonates is low in the Netherlands with properly functioning sewage treatment plants.

Introduction

Phosphonates are molecules with a characteristic C–PO₃H₂ group. Phosphonates are not common in nature (Horiguchi and Kandetsu, 1959, Hilderbrand and Henderson, 1983). Synthetic phosphonates were first prepared more than 60 years before they were found in organisms. Due to their useful properties including good water solubility and stability they are frequently added to domestic laundry and cleaning products to serve as effective sequestrants of metals. They also find an application in wastewater treatment during flocculation and as corrosion and scale inhibitors in industrial cooling and boiling water processes.

In detergent applications four phosphonates HEDP (1-hydroxyethylene-1,1-diphosphonic acid), ATMP (aminotrimethylene-phosphonic acid), EDTMP (ethylenediaminetetra(methylenephosphonic acid)) and DTPMP (diethylenetriamine-pentamethylenephosphonic acid) are used (Gledhill and Feijtel, 1992, Landner and Walterson, 1993). The chemical structures of these phosphonates are depicted in Fig. 1. HEDP is an efficient sequestrant of Ca and in detergent applications it is used to inhibit growth of CaCO₃ crystals on the fabric. ATMP, EDTMP and DTPMP are transition metal chelators and their role is to protect bleaching agents, like perborate, from decomposition. The total volume of these phosphonates was estimated to be 11,000 tons/year in Europe and over 9000 tons/year in the US in the beginning of the 1990s (Gledhill and Feijtel, 1992). Current use volumes in Europe have increased to 12–13 thousand tons/year (Chemical Economics Handbook, 1996). The use of phosphonates in Europe is still developing because of the scrutiny imposed by regulatory agencies on other chelants such as DTPA and EDTA due to their potential of remobilization of heavy metals. The increase in use of phosphonates is also related to voluntary bans of polyphosphates in cleaning applications. Lastly, phosphonates have largely replaced inorganic phosphates in water treatment processes (Chemical Economics Handbook, 1996). Current use volumes in the US have decreased slightly to about 8000 tons/year (Chemical Economics Handbook, 1996). It can be attributed to rising prices of phosphonates and relatively low prices of alternatives such as DTPA and EDTA, the use of which is not scrutinized in the US. The use patterns in the US and Europe differ. In the US phosphonates are mainly used in industrial cooling and boiling water applications while in Europe they are predominantly used in cleaning formulations.

Due to these differences in use patterns the release of phosphonates to the environment in the US and Europe is different. In the US the release is limited and intermittent while in Europe it occurs on a continuous basis. In Europe the use of phosphonates in cleaning products implies “down the drain” environmental exposure via wastewater treatment plants or directly to surface waters. Based on the environmental toxicity and fate data of these substances, Gledhill and Feijtel, 1992, Landner and Walterson, 1993 concluded in their reviews that these chemicals could be used safely at the volumes they considered.

Until recently available analytical methods were insufficient for measurement of concentrations in environmental samples. The development of sensitive analytical methods opened the possibility to compare the results of exposure calculations with measured environmental concentrations (Meerkerk and Puyker, 1997, Nowack, 1997). In addition, this review provides an in-depth discussion of the ecotoxicity data of these phosphonates.

This environmental risk assessment has been made as a part of the voluntarily agreed “Plan of Action Laundry and Cleaning Products” (1990) between the Dutch Soap and Detergent Association (NVZ) and the Dutch Environmental Ministry of Housing, Spatial Planning and the Environment (VROM). In this long-term cooperative project environmental risk assessments of several main components (mainly surfactants) of laundry cleaning formulations were carried out (Van de Plassche et al., 1999). The aim of this paper is to present results of an environmental risk assessment of HEDP, ATMP, EDTMP and DTPMP used in laundry cleaning agents carried out according to the European Union method for the environmental risk assessment of new and existing chemicals (EC, 1996). The risk assessment has been coordinated by the Consultative Expert Group Detergents–Environment (W/M Group) and an extended text of this risk assessment has been published elsewhere (W/M report, 1997). The objective of the W/M Group is to assess technical and scientific data in order to respond to environmental safety questions concerning compounds used in washing and cleaning products. The initiative to set up the W/M Group in the Netherlands was taken after informal discussions between the authorities, the detergent industry and scientists. The members are invited by the W/M Group for their expertise and are professionals in the regulatory, industrial and scientific world.

The total usage of phosphonates remained approximately at the same level in the Netherlands in 1995 and 1998 and is given in Table 1. HEDP and DTPMP are the two most commonly used. Between 1995 and 1998 there was a marked increase in the use of HEDP and decrease in the use of DTPMP due to detergent formulation changes. For example the observed decrease of use of DTPMP is most likely because Procter & Gamble, whose market share in the Netherlands is about 30–40%, has completely replaced DTPMP by a proprietary biodegradable chelator [S,S]-ethylenediamine disuccinate ([S,S]-EDDS) after 1996 (Jaworska et al., 1999). The risk assessment of the phosphonates was carried out based on the volumes from 1998.