Temporal trends of chlorinated paraffins and polychlorinated biphenyls in Swiss soils

Persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), are ubiquitous environmental contaminants that have been targeted by national regulations since the 1970–1980s, followed in 2004 by the worldwide regulation under the Stockholm Convention on POPs. However, concerns are growing regarding the emergence of additional POP-like substances, such as chlorinated paraffins (CPs), which have particularly large production volumes. Whereas short-chain CPs (SCCPs) have recently been restricted in Europe and are currently under evaluation for inclusion into the Stockholm Convention, medium-chain CPs (MCCPs) have received little attention. On the one hand, temporal trends of CPs in the environment have hardly been investigated. On the other hand, the effectiveness of the Stockholm Convention on environmental levels of PCBs is still a matter of debate. Here, we reconstructed temporal trends of SCCPs, MCCPs, and PCBs in archived soil samples from six sampling sites in Switzerland, covering the period 1989–2014 (respectively 1988–2013 for one site). Concentrations of SCCPs have decreased in soil since 1994, which indicates positive effects of the reduction of production of SCCPs in Europe and the increasingly stringent regulation. However, the decline in soil is slow with a halving time of 18 years. Concentrations of MCCPs have continuously increased in soil over the entire period 1989–2014, with a doubling between 2009 and 2014. The concentrations of MCCPs have surpassed those of SCCPs, showing their relevance today, partly as replacements for SCCPs. Soil concentrations of PCBs peaked in 1999, i.e. three decades later than worldwide production and use of PCBs, but earlier than the entry into force of the Stockholm Convention. PCBs follow a decline in soil with a halving time of approx. 8 years. This study shows the usefulness of sample archives for the reconstruction and interpretation of time trends of persistent environmental contaminants.