Jacqueline Horswell is an English-born New Zealand environmental microbiologist who specialises in research into the waste society produces, its effect on the environment, and how it can be managed. Her work focuses particularly on measuring the effect of microbial and chemical contaminants in sewage sludge and the safe reuse of biosolids as fertiliser by the planting of native trees to filter and inactivate pollutants from the sludge and the use of vermiculture. Horswell is involved in consultation with communities in New Zealand and has contributed to official guidelines for the management of biosolids. Her research has also provided information about soil microbial communities for forensic science using microbial cultures and DNA sequencing. Since 2018, Horswell has been a lecturer at Massey University.
Education Horswell completed an undergraduate biology degree at the University of Bath and PhD in microbiology at the University of Aberdeen in 1997. Her PhD thesis was titled Investigation of approaches to accelerate atrazine mineralisation in soil.
Career Horswell moved to New Zealand in 1997 and took up a position as Scientist, Environmental Health Effects, at the Institute of Environmental Science and Research (ESR). In 2008 she took over the biowaste programme at ESR, which later set up and ran the virtual Centre for Integrated Bio Waste Research (CIBR), a collaboration between ESR, Scion, Landcare Research and the Cawthron Institute, to study options for safely and sustainably reusing biodegradable waste. With Horswell as its first programme leader, CIBR was officially launched in 2013 with the purpose of researching how to deal with organic waste, "to make sure, that when it goes on land, this is done safely and does not impact the environment". In July 2018 Horswell left ESR, and her role as Programme Manager for CIBR to become a Senior Lecturer in Water and Waste in the school of Health Sciences at Massey University, Wellington.
Early research Before coming to New Zealand, Horswell worked with Professor Graeme Paton at the University of Aberdeen on biosensor technology involving organisms that can determine whether toxic material is present in soil and identify when sites may have been contaminated by industry or agriculture and when they have been cleaned up. Specifically used in the research was the soil bacterium Rhizobium which because it was sensitive to heavy metals in the soil, could indicate on a biosensor light whether or not the soil was healthy. She applied this knowledge early in her time with ESR, in particular determining the impact of heavy metals in sewage sludge on microbes in the soil. In 2000 Horswell was commissioned to do a report for the New Zealand Ministry of Health, Ministry for the Environment and Industry on the bioavailability of organic forms of arsenic to plants, and ultimately people in the soil-plant-human route, as a result of its use in the treatment of timber. The report which was a review of the literature, concluded that because salts of copper, chromium and arsenic have been used in New Zealand on the preservation of wood, "treatment sites can become highly contaminated with these metals, especially arsenate".
Managing biosolids in the environment The possible re-use of biosolids as fertiliser has been a key area of study for Horswell and in 2008, she recommended research priorities to the 2008 Annual Conference of the New Zealand Land Treatment Collective. Some of the key recommendations for potential projects included: "Environmental fate of biosolids and effluent-borne pathogens in sewage treatment systems...[monitoring]...source control of nutrients i.e. washing powder etc...[determining the]...effect of emerging contaminants such as endocrine inhibitors and pharmaceuticals on the environment. A 2009 study, in which Horswell was involved, investigated the degree that sludge-born pathogen organisms survive and are transported in soils and affect surrounding water. The paper noted the importance of sewage treatment and disposal in protecting a community from pathogens and that while sewage sludge is a valuable resource with plant nutrients that can be directly applied to land as fertiliser, and pathogen numbers are reduced during sludge processing, it is unlikely that they can be completely eliminated, and need to be controlled via "guidelines and regulations that set criteria for levels of pathogens, which are protective of the environment and human health." In 2017, Horswell participated in research looking at the possible use of biosolids to reforest areas where the soil had been degraded. The thesis was that because many New Zealand native plant species thrive in low-fertility soils, they may respond well to biosolids which would, in turn, improve the soil microbial activity. The report concluded that after adding biosolids to the soil, all the NZ-native species showed either improved growth or an increase in nutrient status, but cautioned that further testing was required to investigate the possible long-term effects of this. Horswell co-authored a research report that evaluated the evidence that blending biosolids with organic materials could reduce the environmental impact on the soils and concluded that while it is not always a viable solution, "combining biosolids with other organic wastes to rehabilitate degraded land remains a potentially practicable and sustainable management of these resources."
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