Estimating human toxicity potential of land application of sewage sludge: the effect of modelling choices

Abstract

Purpose Many municipalities are facing increasing pressure to adapt solid waste and wastewater management infrastructures in order to better close nutrient cycles. The focus of this study is on the estimation of the human toxicity potential associated with chemical contaminants released upon the application of sewage sludge to agricultural land. More specifically, this study investigated the effect of modelling choices regarding fate and exposure assessment. Methods Monitoring data were collected for contaminants present in the sewage sludge from the wastewater treatment plant in Gothenburg and from other municipal wastewater treatment plants in Sweden. Based on these monitoring data, an overall burden of disease was estimated using characterisation factors taken from the USEtox models (versions 1.01 and 2.0). For the exposure through vegetables, an alternative life cycle impact assessment (LCIA) model was developed. The intake fractions thus obtained were used in combination with human health effect factors taken from the USEtox 2.0 database. The model results were compared with the USEtox models, and whether these two versions of the USEtox model provide significantly different results was also examined. The potential relevance of accidental ingestion of sludge was also considered.Results and discussion The different LCIA models provided burden of disease estimates that differed from one another for individual contaminants (up to five orders of magnitude). The aggregated burdens of disease (i.e. sum for all contaminants considered in this study) estimated through different model variants, however, were of the same order of magnitude. For both metals and organic contaminants, only a small set of contaminants was found to make significant contributions to the aggregate burden of disease. However, it is uncertain whether the 15 metals and 106 organic contaminants covered by this study are those of greatest health significance of all contaminants potentially present in sewage sludge. Conclusions and recommendationsThe results of this study indicate that the technical information provided by the various approaches to modelling human toxicity in life cycle assessment (LCA) in the context of land application of sewage sludge management is consistent on the whole. However, given the uncertainties associated with the assessment of human toxicity in LCA, it is important to also contemplate the extent to which LCA in general is capable of informing the sewage sludge debate when it comes to human toxicity and possibly also other indicators. Future research could focus on identifying which types of questions of interest in the context of sewage management can be answered by LCA and which cannot.

Trace contaminants in the environmental assessment of organic waste recycling in agriculture: Gaps between methods and knowledge

“…All of these studies carried out using USES-LCA to assess terrestrial ecotoxicity inevitably inherit the shortcomings of that model, including the lack of ability to extrapolate aquatic data to estimate terrestrial ecotoxicity. Harder et al (2017) studied the USEtox-modelled effects on human toxicity and compared the results with regard to sludge spread on soil. In the context studied, 13 organic contaminants were found to be of greatest potential concern, including bis(2-ethylhexyl) phthalate, hexachlorobenzene, 1 PCB, 1 polybrominated diphenyl ether, 17α-ethinyloestradiol, 7 PAH and one biocide (Mirex, CAS No.…”

Improved life cycle modelling of benefits from sewage sludge anaerobic digestion and land application

“…The environmental impacts of sludge use in agriculture have recently attracted attention in several modelling studies, e.g. for toxicity assessments (Harder et al, 2016) and pathogen risk (Harder et al, 2014). Heimersson et al (2016) showed that the modelling of N, P and major C flows originating from the wastewater is very important in LCA, since the type of wastewater treatment process determines whether they end up as an emission, contributing to environmental impacts, or as a resource flow and thereby possibly lowering or counteracting environmental impacts from the assessed system.…”

Soil properties and microbial ecology of a paddy field after repeated applications of domestic and industrial sewage sludges

“…The land application of sludge involves effects on soil properties, soil microbes, plants, and animal by the accumulation of these pollutants. This may threaten the safety of agricultural production and human health through the food chain (Pritchard et al 2010;Bondarczuk et al 2016;Harder et al 2016). Thus, the use of sewage sludge as a source of plant nutrients for crop production needs to be carried out carefully to protect the environment and human health.…”