NEWS
FOOD & AGRICULTURE
Fertiliser from dairy waste
ANTHONY KING
Scientists in Israel say they can convert dairy wastewater into phosphorus fertiliser. The researchers at Tel Hai College and MIGAL Institute
HEALTH & WELLBEING
Telomere shortening and stress
ANTHONY KING
Telomeres are DNA-protein structures at the tails of chromosomes, which are thought to act as a molecular clock on ageing. Each time a cell divides, the telomeres shorten a bit, and when they become critically short the cell’s ability to divide is impaired. Now, a recent meta-analysis study has found that junior doctors undergo six times the typical level of telomere shortening, believed to be due to long working hours and stress (Biological Psychiatry, doi:10.1016/j. biopsych.2019.04.030). ‘The first year as a doctor is universally considered one of the most stressful years. It’s the first time they have real responsibility. They work long hours, may be sleep deprived and be the primary care giver for really sick people,’ says study leader Srijan Sen, psychiatrist at the University of Michigan, US. The 250 interns were part of the
Intern Health Study, which has been running for 12 years and follows thousands of interns in 90 hospitals across the US. Previously it recorded subjective markers of stress and found high rates of depression during the first year of internship. ‘The findings fit nicely with our paper earlier this year showing that telomeres are reducing in patients with schizophrenia and bipolar disorder, reporting high levels of childhood trauma,’ comments Ole Andreassen, psychiatric geneticist at the University of Oslo, Norway, adding
that the ‘biological mechanisms between stress and telomere length need further clarification.’ There is emerging evidence for
shorter telomeres being a risk factor for psychiatric disorders, as well as disorders such as heart disease and stroke. There was, however, too much variation between individuals for telomere length measurement to be useful as an individual predictor. The most surprising aspect of the study, says geneticist Jean-Baptiste Vannier at Imperial College London, UK, ‘is the fast effect of stress on telomere size, since only one year was spent between the two telomere length analyses.’ He describes telomeres as ‘almost
like a timer counting down before death… Before being established as a health biomarker for every individual, we still need to understand which critical point needs to be reached to ascertain when an individual is presenting more risk for obesity, cancer or death.’ Each individual and every cell starts with a different telomere size, which is a complicating factor. Indeed, biologist Predrag
Slijepcevic at Brunel University, London, says that what matters from an ageing perspective is not the average length of telomeres, but the set of shortest telomeres in the genome. Recent research suggests that results obtained with the qPCR DNA amplification technique, used in this study, should be validated by another method and at a separate lab.
began by treating dairy wastewater to remove suspended solids, using nanocomposite technology (Soil Sci. Soc. Am. J., doi:10.2136/sssaj2018.07.0278). They then took aluminium waste treatment residue, which is normally buried in landfill, and added it to the treated dairy waste. This aluminium-rich residue has a high surface area and a strong affinity for organic ions and inorganic phosphorus. Dairy wastewater comes from treating cows’ udders, as well as runoff from their urine. The process involves recapturing phosphorus in wastewaters using the aluminium treatment residue and organic matter to generate a material that, when sun dried, can be applied to crops as an alternative phosphorus fertiliser. ‘We mixed the aluminium waste treatment residue
with dairy effluents for three days,’ explains senior study scientist Iggy Litaor at Tel Hai College in Israel. ‘You cannot spread untreated dairy wastewater on the ground because you may contaminate groundwater, streams and soil [since] dairy wastewaters contain extremely high sodium concentrations.’ Unlike nitrogen, which can be taken from the air, phosphorus is limited to terrestrial deposits, with supplies expected to run out in the next 100 to 200 years. The researchers added nitrogen, phosphorus and potassium and minor nutrients such as iron and zinc to generate a fertiliser tested on lettuce. The results indicate that the alternative phosphorus fertiliser performed as well as commercialised NKP fertiliser. The concentrations of aluminium in the soil leachate
were below detection levels, says Litaor, with between 1 and 3.1g/kg in the lettuce leaves. However, soil scientist Martin Blackwell at Rothamsted Research says that he has ‘concerns that applying large quantities of aluminium to soils could result in soil contamination and plant uptake under the wrong conditions [such as in acids soils]’.
Uzkurt Juho at Aalto University in Finland, who
has worked on phosphorus recovery from municipal wastewater sources as part of his PhD, says that the most important factor in techniques to recover phosphorus is the economics, which ‘is difficult to assess from lab/ pilot studies’. The article spoke nothing about possible pollutants or hygienic quality of the end product. [But] the hygiene quality of the end product would need to be proven for this to work in the EU. The process reportedly removed between 50 and 95% of the phosphorus from the waste stream. The researchers are now doing more detailed economic analysis of their system. ‘A rough estimate made by my grad student suggests that a mid-size cowshed [300 cows] may produce 180t/year of fertiliser,’ notes Litaor. ‘Larger sized cowsheds [1000 cows] may increase the amount of fertiliser by four to five times.’
06 | 2019
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LAGUNA DESIGN / SCIENCE PHOTO LIBRARY
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