Tracking pollution sources in groundwater tracers

Emerging organic contaminants (EOCs) and environmental DNA (eDNA) are innovative tools that can be used to identify sources of pollution in groundwater.

Using these tools, a team of ESR scientists is analysing the presence of EOCs and the diversity of species through eDNA, to build a predictive model for pollution source identification and aid targeted mitigation.

The problem

Groundwater provides us with baseline flow for our rivers and streams, 40% of Aotearoa New Zealand’s drinking water, irrigation of agriculture and horticulture and is of high cultural and recreational importance. Nitrate is a major pollutant of groundwater in Aotearoa New Zealand.

Although natural processes occur in the environment that produce nitrate as a part of the nitrogen cycle, human activity is unbalancing this cycle, which means nitrate ends up in our waterways and groundwater. The main source of nitrate that leaches into groundwater is from fertilisers used in agriculture, but other sources such as leaking sewage pipes, on-site wastewater management systems, landfills, and municipal wastewater systems also contribute to nitrate pollution. This makes it challenging to differentiate pollution sources and manage them effectively in catchments with multiple potential sources.

Determining a better measure of the source of contaminants in groundwater can enable a targeted response in mitigating the risk. In Aotearoa New Zealand, emerging organic contaminants (EOCs) have been recently detected in groundwater, and their presence can be used to track pollution sources. EOCs act like a chemical fingerprint and have been previously used in sources (such as wastewater treatment plants and septic tanks) in other countries. ESR scientists are using the same methods to differentiate sources of contamination in Aotearoa New Zealand.

Environmental DNA (eDNA) analysis provides insights into the biological diversity of various environments. While its use has primarily focused on larger species, eDNA analysis is now being extended to smaller, single-celled organisms. The combination of EOC analysis and eDNA analysis can help in the identification of specific sources of pollution and inform effective management strategies to protect groundwater quality.


Environmental DNA (eDNA) refers to the genetic material shed by organisms into their environment, like water or soil. This genetic material can be extracted from environmental samples and analysed to identify the presence of different species without direct observation. eDNA analysis has become increasingly popular in recent years for its potential applications in biodiversity assessments, ecological monitoring, and invasive species detection.

The process of eDNA analysis typically involves collecting environmental samples such as water, soil or sediment, filtering and extracting the DNA from the sample, and sequencing the DNA to identify the species present. This can provide a non-invasive method of detecting species in a particular place, especially for species that are difficult to detect through traditional survey methods. eDNA analysis has been used in a variety of settings, from monitoring fish populations in rivers and lakes, to detecting rare or endangered species in remote environments. However, like any technology, there are limitations and challenges associated with eDNA analysis, including issues of sensitivity, specificity, and interpretation of results.

The solution 

Led by Dr Andy Pearson, Dr Louise Weaver and a team of chemists, microbiologists and environmental scientists, the primary goal of this project is to use EOCs and eDNA to identify and delineate pollution sources.

To achieve this, the ESR team will analyse groundwater that is close to different types of pollution sources and measure the presence of EOCs and eDNA at the point of discharge, such as from on-site wastewater management system (OWMS) outflows.

This model will help effective management and regulation of pollution by allowing regional councils to detect sources of contamination, especially in catchments with multiple potential sources.