Abstract
The use of sludge in agriculture has been encouraged as a means of increasing soil nutrient content and improving the water holding capacity. On the negative side, major public health concerns with sludge application prevail, mainly due to the high concentration of pathogenic microorganisms. Soil-transmitted helminths (STHs) are of major health concern in this regard, especially in endemic regions, mainly due to the high environmental resistant of the eggs combined with a low infectious dose. In this study the concentration of STH eggs in two months dried sludge from Durban, South Africa and Dakar, Senegal was determined and compared. Sampling was carried out from January to October 2016 and in September 2016 for Dakar. Ascaris spp, hookworm, Trichuris spp, Taenia spp and Toxocara spp were the commonly recorded STH eggs. STH egg concentrations were higher in Dakar than in Durban, with viable STH egg concentrations exceeding both local and international guidelines. Due to the high concentration of viable STH eggs, risks of Ascaris spp infection was very high for farmers applying this sludge on their farms in both Durban (7.9 × 10−1 (±1.7 × 10−2)) and Dakar (9.9 × 10−1 (±1.3 × 10−5)). Consumption of lettuce grown on sludge amended soil will result in probable infections but harvest after 30 days between sludge application and harvest in Durban gave median probability infection risks with a risk level similar to the WHO tolerable risk value (10−4). This time period need to be prolonged to harvest in Dakar to 40 days to reduce the risks of infection to the tolerable risks values. Further treatment of the sludge either through composting or drying for longer periods of time is thus recommended from a public health perspective.
Highlights
Application of faecal sludge on agricultural lands is a major component of resource recovery, aimed to ensure that vital plant nutrients are returned to the soil
Hookworm, Trichuris spp, Taenia spp and Toxocara spp were detected in sludge from the two wastewater treatment plants (WWTPs) in Durban
The difference between the total and viable Soil-transmitted helminths (STHs) egg concentrations was statistically significant for all the types of eggs detected except for Taenia spp and Toxocara spp
Summary
Application of faecal sludge on agricultural lands is a major component of resource recovery, aimed to ensure that vital plant nutrients are returned to the soil. Sludge is high in organic matter and nutrients (Hernandez et al, 2017), making it a valuable amendment in restoring degraded, exhausted (Jimenez and Alvarez, 2005) and burned soils (Guerrero et al, 2007), as well as improving fertility and crop productivity (Bittencourt et al, 2013). It may increase the water holding capacity of soil Poor sanitation and faecal contamination result in an enhanced transmission and a high prevalence in developing countries, where faecal sludge is a main contributing factor (67e735 eggs/g total solids (TS)) (Feachem et al, 1983; Strauss et al, 2003; Jimenez and Wang, 2006) as compared to more developed countries (2e13 eggs/ g TS) (Jimenez et al, 2002)
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