SEPTEMBER 2017 RESEARCH UPDATE
Here we go again, another paper suggesting that the sky will fall as a result of biosolids application. And, to prove their point, they actually used the falling sky -- a/k/a simulated rainfall.
The first paper in the library reports on runoff from biosolids amended plots in eastern Colorado where agronomic rates of biosolids were applied. Equipment was used to create a 100-year rain event, and runoff was collected from the plots. This was done once, prior to biosolids application, and three times afterwards, all within a 30-day period. Anthropogenic waste indicators (AWIs), a potential alternative name for TORCs (toxic organic compounds) or PPCPs (pharmaceutical and personal care products) or microconstituents, were measured. The concluding sentence of the abstract can send shivers up your spine, if you are so inclined: ‘For 14 of 17 compounds examined, the potential for runoff remobilization during rainstorms persists even after three 100-year rainstorm-equivalent simulations and the passage of a month.’ So, what is the best way to deal with this?
A great way to start is by looking at more than the catchy sentence. If you start with the abstract in its entirety for example you will find out that the authors actually tested for 69 compounds. Eighteen of those were not included in the final evaluation because they were found in the soil before the biosolids had been applied. Another 34 were close enough to detection that they were also left out. In other words, that catchy sentence would be a lot less catchy if it read ‘For 14 of the 69 compounds examined….’.
If that isn’t enough to calm you down, it is always good to start with the methods section of the paper. In this case the authors site a previous paper for the methods (# 2 in this library) so let’s take a look -- same plots and same design for both papers. The plots were 2 x 3 meters, and biosolids were applied at agronomic (low and reasonable rates) of 3.5 tons per hectare. Water was applied at the equivalent of a hundred year event for that area (Eastern CO) which is the equivalent of 65 mm per hour. The authors measured concentrations of the compounds (nanograms per liter or parts per trillion), and the number of liters of water that eroded off of the plots. The first thing that I did was calculate how much water would be added to the each plot in a 65 mm per hour storm. The answer is 390 liters, or an awful lot of water bottles’ worth.
After the methods, it is time to look at the actual data. Here I looked at paper # 2 first. The focus of this was hormones. Data is shown from the runoff events before biosolids application, and at days 1, 8 and 35 after biosolids application. If you look at the data, the first thing that stands out to me is that the water wasn’t exactly flooding off of the plots. On day 1, the maximum runoff rate, reached after 40 minutes of rainfall, topped of at 1 liter per minute. On Day 8, the runoff rate was higher and started sooner, topping off at 4 liters per minute at 30 minutes. By the last event, the runoff was down to 2 liters at 40 minutes. So, when you are looking at the concentration data you need to remember that the highest volume of runoff was 4 liters per minute, reached well into the rainfall event, from a simulated 100- year storm with total water applied of 390 liters per hour. In other words, we are not talking about needing to build an ark.
From here we can look at the concentrations in the runoff water. The hormone paper tested for 12 compounds. Results are presented for each compound as well as for the sum of all compounds tested. If you just look at the numbers on the y-axis, you can see that the mass loads of the hormones sum to 500 on some of the plots for the first day and on all three on day 8. They are down to 200 by day 35. Five hundred sounds like a lot, but then you have to remember the units that are being used. Five hundred parts per trillion is the same as 0.5 parts per billion or 0.0005 parts per million. That is the sum of all measured hormones at the highest runoff rate from these plots. So, even though the 500 is ng per minute, we are talking about the worst case of the worst case of the worst case.
While the authors have managed to show that with all of these worst cases, you are able to detect hormones, what they have not shown is any environmental significance of this result. That is often not how results are talked about. Typically, they are put in the ‘sky is falling’ category.
If you go back to the first paper, knowing the methods and the context, what do you see?
The key figure is right there and based on the discussion of the first paper (#2 in the library), I’ll bet you can see that it is pretty much the same deal. Low levels of total water running off the plots and minute, though above detection, concentrations of the 14 compounds that they were able to quantify. Remember, that is of the original 69 compounds.
Many of the people that get upset by these studies have not put them into the appropriate context. The general misunderstanding is that the wastewater treatment process rather than home use is responsible for the release of these compounds into the environment. Show those people the 3rd paper in the library.
The third is a review paper that compares concentrations of a wide range of these AWIs in septic systems and wastewater treatment plants. Concentrations in septic tanks and drain fields are compared with treatment plants. You can see that the concentrations in the septic tanks are typically higher than concentrations in the wastewater plants. Wastewater treatment is not the devil. Those people with headaches who like a cup of coffee in the morning are the real culprits.
The last two papers in the library are meant to put all of this into a less hysterical, more real-world context. They focus on results from manure applications. The first looks at hormone movement from simulated rainfall from manure-amended soils in reduced-till, conventional-till and no-till cultivation at 1 and 30 days after manure application. They show the actual rainfall that occurred over the study period in addition to the simulated rainfall. They show the percentage of total hormones applied that have run off. The take home message here is that movement of hormones is lowest with no-till, and the movement with no-till occurred only at the first sampling time. What we learn here is that cows have hormones, too, and that management practices can reduce any potential for runoff from biosolids- or manure-amended soils.
The final paper looks at different types of manures applied to frozen soils and looks at runoff on a watershed level of nitrogen, phosphorus, cations and estrogen. A take home sentence, taken from within the text: “In combination, these findings indicated that similar rates of application of manure to frozen, mature, grassland with an ~10% slope pose little risk of environmental harm from runoff, and support the use of vegetative buffer strips in proximity to waterways’.” The authors found that total runoff per hectare from January through April topped off at 220 liters from one of the treatments. Other treatments showed as little as <1 liter of runoff per hectare. They also showed that movement of N and P is more of a concern than the dregs from your cup of coffee. The authors present the total estrogen (E2) equivalent per hectare for the same experimental period, both as total loading and as a percentage of applied. This ranges from 0.036% to 0.2% with a corresponding total of 848 and 112 mg of estrogen moved per hectare. The amount of nitrogen moved was 218 kg, or 218,000,000 mg, for the same treatments.
In other words, the sky is not falling. You can still drink coffee. And if you are concerned about movement of AWIs from biosolids, you would do well to follow the regulations developed to prevent nutrient movement from applied fields.
Sally Brown, University of Washington