Recycling fertilisers from human excreta exhibit high nitrogen (N) fertiliser value and result in low uptake of pharmaceutical compounds, new research has found.

Recycling fertilisers (RFs), and particularly nitrified urine fertilisers (NUFs) alone or in combination with fecal compost have been found to be “viable alternatives” to commercial fertilisers.

The risk for human health of contamination with pharmaceutical compounds from fecal compost application appears to be low, researchers said.

Research published in the Frontiers in Environmental Science today (Monday, January 16) shows the results of a field experiment in Berlin at the Leibniz Institute of Vegetable and Ornamental Crops.

Using locally available resources such as human excreta to produce bio-based recycling fertilisers can substitute mineral fertilisers and promote environmentally friendly food production, the researchers said.

Fertiliser experiment

In recent years, novel RFs produced from biological or chemical processing of organic waste stream to recover nutrients have become increasingly established, the researchers said.

The results using human-waste fertiliser were compared against the commercial, organic fertiliser vinasse, which is a by-product of the biomass distillation from sugar, starch crops or cellulosic material.

White cabbage was cultivated in plots in three different soil types – sand, loam or silt – and treated with two NUFs and one fecal compost alone or in combination.

The N fertiliser value of the NUFs used in the field experiment was comparable to vinasse, and, in combination with fecal compost, resulted in comparable cabbage yields.

Research shows that the highest yield was recorded from the sandy soil, where vinasse and NUF treatments led to comparable yields as expected in organic productions systems.

The combined application of NUF and compost led to slightly lower crop yields, but may increase soil carbon content in the long term, promoting climate-friendly food production, the researchers said.

Pharmaceutical compounds

A wide range of chemical compounds from pharmaceuticals to insect repellants were found in the first target screening of the fecal compost sample.

Of 310 target compounds screened for, 20 substances were detected with 11 being pharmaceutical compounds, the researchers found.

In the second screening approach, involving a smaller and adapted set of target compounds, 11 of the 21 tested compounds were below the limit of detection (LOD).

Low levels of ibuprofen appeared in the adapted solid phase extraction method, however cabbage plants contained only traces of carbamazepine and ibuprofen.

Plant uptake of pharmaceuticals was higher in sand than in loam, and concentration in the edible part was lower than in the outer leaves, results show.

However, the effect of the pharmaceutical substances on the soil systems was not assessed in this study.

The consequences of long-term application of fecal compost requires further investigation, particularly regarding the preservation of soil multi-functionality, the researchers said.