Scientific Studies of Sewage Sludge

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WARNING! Sewage sludge is toxic. Food should not be grown in "biosolids." Join the Food Rights Network.


This article is part of the Food Rights Network, a project of the Center for Media and Democracy. Find out more here.

Scientific studies of sewage sludge confirm its hazards. A list of just some of the hazardous chemicals and pathogens found in sludge can be found in the article Sludge contaminants. Sludge contaminants include Dioxins and Furans, Flame Retardants, Metals, Organochlorine Pesticides, 1,2-Dibromo-3-Chloropropane (DBCP), Naphthalene, Triclosan, Nonylphenols, Phthalates, Nanosilver, and thousands more substances.

Some select studies and technical papers are below. NOTE: A PDF version of each study is attached wherever possible.

After sewage sludge fertilization of "acid pine forests (Pinus sylvestris L.) on sandy soils in a south to north temperature gradient in Sweden," some research areas saw "a limited increase of Cr, Cu, Ni, Zn both in the humus and in the upper mineral layers."
"Based on previously published hydroponic plant, planktonic bacterial, and soil microbial community research, manufactured nanomaterial (MNM) environmental buildup could profoundly alter soil-based food crop quality and yield. However, thus far, no single study has at once examined the full implications, as no studies have involved growing plants to full maturity in MNM-contaminated field soil. We have done so for soybean, a major global commodity crop, using farm soil amended with two high-production metal oxide MNMs (nano-CeO2 and -ZnO). The results provide a clear, but unfortunate, view of what could arise over the long term: (i) for nano-ZnO, component metal was taken up and distributed throughout edible plant tissues; (ii) for nano-CeO2, plant growth and yield diminished, but also (iii) nitrogen fixation—a major ecosystem service of leguminous crops—was shut down at high nano-CeO2 concentration. Juxtaposed against widespread land application of wastewater treatment biosolids to food crops, these findings forewarn of agriculturally associated human and environmental risks from the accelerating use of MNMs." (Emphasis added.)
This study was also summarized in Science News here and in ScienceNow here.
"The anti-microbial substance triclosan can partition to sewage sludge during wastewater treatment and subsequently transfer to soil when applied to land. . . . Triclosan and methyl-triclosan concentrations were measured in soil samples collected monthly from three depths. A large fraction of triclosan loss appeared to be explained by transformation to methyl-triclosan. After 12 months less than 20% of the initial triclosan was recovered from each soil. However, the majority was recovered as methyl-triclosan. Most of the chemical recovered at the end of the experiment (both triclosan and methyl-triclosan) was still in the top 10 cm layer, although there was translocation to lower soil horizons in all three soils."
"In this work, the degradation of anionic and non-ionic surfactants in agricultural soil amended with sewage sludge is reported. The compounds analysed were: linear alkylbenzene sulphonates (LAS) with a 10–13 car- bon alkylic chain, and nonylphenolic compounds (NPE), including nonylphenol (NP) and nonylphenol eth- oxylates with one and two ethoxy groups (NP1EO and NP2EO). . . . Environmental risk assessment revealed that for LAS homologues no environment risk could be expected after 7 and 8 days of sludge application to the soil for 22.4 and 12.7 °C, respectively; however, potential toxic effects could be observed for the nonylphenolic compounds during the first 56 days after sludge application to the soil" (emphasis added).
"There are so many potentially harmful substances found in sludge particularly heavy metals (cadmium, chromium, lead, nickel, copper, mercury, zinc, iron and aluminum) . Many are known to cause cancer and other diseases. Certain compounds found in sludge have been identified to harm the reproductive systems of fish and other aquatic life. These contaminants need to be cleaned up for a safe environment. An experiment was conducted to evaluate the potential of Acacia mangium as a phytoremediator to absorb heavy metals from sewage sludge contaminated soils. Acacia mangium seedlings were planted on six different growth media (soil + sludge) were: T0 (100% soil, control), T1 (80% soil+20% sludge), T2(60% soil+40% sludge), T3(40% soil+60% sludge), T4(20% soil+80% sludge) and T5(100% sludge). The highest growth performance such as height, basal diameter and number of leaves was found in 40% soil+60% sludge. Cadmium (Cd) and lead (Pb) were highly concentrated in the stems, chromium (Cr) and copper (Cu) in the roots, while zinc (Zn) was concentrated in both leaves and stems. A. mangium seems to have a high potential to absorb high amounts of Zn, Cd, Pb, Cr and Cu in the leaves, stems and roots. A. mangium showed high translocation factor and low bioconcentration factor values in the sludge contaminated soil as well as it was able to tolerate and accumulate high concentrations of heavy metals. The roots of A. mangium were found to be suitable for the absorption of heavy metals in contaminated soils. Therefore, this species can be a good phtyoremediator for sewage sludge contaminated soil and to mitigate soil pollution." The study does not address how to dispose of the contaminated Acacia plants after the phytoremediation of the bioaccumulated heavy metals.
"The potential presence of steroid hormones in runoff from sites where biosolids have been used as agricultural fertilizers is an environmental concern. A study was conducted to assess the potential for runoff of seventeen different hormones and two sterols, including androgens, estrogens, and progestogens from agricultural test plots. The field containing the test plots had been applied with biosolids for the first time immediately prior to this study. . . . Overall, these results indicate that rainfall can mobilize hormones from biosolids-amended agricultural fields, directly to surface waters or redistributed to terrestrial sites away from the point of application via runoff. Although concentrations decrease over time, 35 days is insufficient for complete degradation of hormones in soil at this site" (emphasis added).
"Triclosan (TCS) and triclocarban (TCC) are widely used broad spectrum bactericides that are common pollutants of waterways and soils. Methyl triclosan (mTCS) is the predominant bacterial TCS metabolite. Previous studies have shown that TCS disrupts thyroid hormone (TH) action; however, the effects of mTCS or TCC are not known. . . . mTCS and TCC affected TH-responsive gene transcripts at the highest concentration in mammalian cells, whereas a modest effect included lower concentrations in the C-fin assay. In contrast, TCS did not affect TH-responsive transcripts. These results identify nontarget biological effects of these bacteriocides on amphibian and mammalian cells and suggest the TH-disrupting effects observed for TCS could be mediated through its metabolite. . . . Given the observed effects in cell and organ culture, examination of the effects of TCC on postembryonic development of frog tadpoles and on intact mammals is warranted."
"As polybrominated diphenyl ethers (PBDEs) face increasing restrictions worldwide, several alternate flame retardants are expected to see increased use as replacement compounds in consumer products. Chemical analysis of biosolids collected from wastewater treatment plants (WWTPs) can help determine whether these flame retardants are migrating from the indoor environment to the outdoor environment, where little is known about their ultimate fate and effects. The objective of this study was to measure concentrations of a suite of flame retardants, and the antimicrobial compound triclosan, in opportunistic samples of municipal biosolids and the domestic sludge Standard Reference Material (SRM) 2781. . . . The biosolids and SRM 2781 were analyzed for PBDEs, hexabromobenzene (HBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB), di(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH), the chlorinated flame retardant Dechlorane Plus (synand anti-isomers), and the antimicrobial agent 5-chloro-2-(2,4-dichlorophenoxy)phenol (triclosan). PBDEs were detected in every sample analyzed, and ΣPBDE concentrations ranged from 1750 to 6358 ng/g dry weight. Additionally, the PBDE replacement chemicals TBB and TBPH were detected at concentrations ranging from 120 to 3749 ng/g dry weight and from 206 to 1631 ng/g dry weight, respectively. Triclosan concentrations ranged from 490 to 13,866 ng/g dry weight. The detection of these contaminants of emerging concern in biosolids suggests that these chemicals have the potential to migrate out of consumer products and enter the outdoor environment."
    • Biosolids amendment increases soil metals over 25 years later.
    • Douglas-fir growth benefits fail to materialize from biosolids amendments.
    • Phytochelatins are elevated in foliage of trees and roots of greenhouse seedlings after new biosolids are added to soil.
    • Biosolids connected to metal stress in Douglas-fir.

"Thousands of high production volume (HPV) chemicals are used in the US at rates exceeding 450 000 kg (1 million pounds) per year, yet little is known about their fates during wastewater treatment and upon release into the environment."

"Any pharmaceuticals and personal care products (PPCPs) are commonly found in biosolids and effluents from wastewater treatment plants. Land application of these biosolids and the reclamation of treated wastewater can transfer those PPCPs into the terrestrial and aquatic environments, giving rise to potential accumulation in plants."

"Nanosized silver sulfide (R-Ag2S) particles were identified in the final stage sewage sludge materials of a full-scale municipal wastewater treatment plant using analytical high-resolution transmission electron microscopy. The Ag2S nanocrystals are in the size range of 5-20 nm with ellipsoidal shape, and they form very small, loosely packed aggregates. This study suggests that in a reduced, S-rich environment, such as the sedimentation processes during wastewater treatment, nanosized silver sulfides are being formed. This field-scale study provides for the first time nanoparticle-level information of the Ag2S present in sewage sludge products, and further suggests the role of wastewater treatment processes on transformation of Ag nanoparticles and ionic Ag potentially released from them."

Sewage sludge tests revealed 49 organohalogens present, by using methods of gas chromatography with electron capture negative ionization mass spectrometry; 23 of those were identified as flame-retardants: "Evaluations of the risks associated with biosolids land-application...for future environmental fate".

Two sediment cores from a wastewater-impacted depositional zone of the Mississippi River were analyzed. 2,8-DCDD and three other dioxin congeners triclosan-derived dioxins present. The total dioxin pool "increased to as high as 31% by mass in recent years, indicating that their contribution to total dioxin toxicity may need consideration".

This study shows that AC materials can catalyze transformation of secondary amines to yield trace levels of of N-nitrosamines under ambient aerobic conditions. These results show that "selecting ACs and reaction conditions are important to minimize analytical errors and undesirable formation associated with nitrosamines in water samples".

The main purpose of this study was to investigate the occurrence of vancomycin resistant enterococci (VRE) in treated sewage sludge. This study "demonstrated widespread occurrence of VRE in sewage sludge in the studied WWTP". This indicates a “risk of antimicrobial resistance being spread to new farms and to the society via the environment if the sewage sludge is used on arable land”.

The main purpose of this study was to investigate the polybrominated diphenylethers (BDEs) transfer from feed to cows’ milk. The fate of tri- to hexaBDEs in lactating cows exposed to a naturally contaminated diet was studied by analyzing feed, feces, and milk samples from a mass balance study. The behavior of the tri- to hexaBDEs was "consistent with that observed for other classes of halogenated aromatic contaminants such as PCBs and PCDD/Fs".

Many of the 145 chemicals tested for were current nationwide. Biosolids from all of the 74 large treatment plants surveyed had same 27 metals, but only zinc, molybdenum, and nickel surpassed standards for application to fields. Almost all of the 11 flame retardants on the list were there in every sample.

The results of this survey indicate that "27 metals were found in virtually every biosolids sample". Four of six semivolatile organics and polycyclic aromatic hydrocarbons were found in at least 72 samples. "All off the flame retardants except one [(BDE-138)] were essentially found in every sample; [BDE-138] was found in 54 out of 84 samples".

This study focuses on the investigation of agricultural soil near Decatur, Alabama., Scientists with the EPA, USDA, and FDA are investigating if perfluorinated chemicals have entered the human food chain and contaminated meat. They suspect that "PFOA and PFOS, treated municipal sewage sludge, or biosolids, were applied to some 5000 acres of agricultural land".

Scientific literature of polybrominated diphenyl ethers(PBDEs) and polybrominated biphenyls(PBBs) in sewage sludge and a survey of these compounds in sewage sludge from 16 Australian wastewater treatment plants. This study presents "need for a risk assessment of PBDEs in sewage sludge used for land application".

Study looks at the "fate of 14C-labelled p353-nonylphenol (NP) in soils amended with differently treated sludges originating from the same precursor". Nonylphenol was degraded much faster in soils modified with liquid sludge, while a major portion of it was intact and extractable by organic solvents when sludge had been centrifuged prior to soil amendment.

In this study, the presence of seven pharmaceuticals and one antibacterial was evaluated using ultrasonic extraction and liquid-chromatography tandem mass spectrometry (LC–MS/MS). During the experiment…elimination was found for tetracycline, doxycycline, clindamycin, erythromycin, and clarithromycin.

Survey looks at the use of a model wastewater treatment plant for removal of oxide nanoparticles. “Investigation on the agglomeration of oxide nanoparticles in wastewater streams revealed a high stabilization of the particles against clearance (adsorption on the bacteria from the sludge)”.

Nanoparticles should bound in the sludge and not represent a setback in the aqueous effluent. However, new study on the ceramic model material cerium dioxide found that a major “amount was able to leave an experimental sewage works and therefore could possibly enter bodies of water”.

This study indicates that “The Environmental Protection Agency must gather data on the toxicity of spreading sewage sludge”. Results show that “The Environmental Protection Agency must gather data on the toxicity of spreading sewage sludge”.

Study about a Farmer Andy McElmurray who “won his court case against the US Department of Agriculture over land poisoned by sludge fertilizer."

Report on the results of experiments examining the partitioning and persistence of PrPtse during simulated wastewater treatment processes including activated and mesophilic anaerobic sludge digestion.

The purpose of this study was to test the presence and fate of Pharmaceutical and Personal Care Products (PPCP's) in the environment from three wastewater treatment facilities in Northwest Ohio, USA. The greatest number of toxic compounds "were found in the influent from the largest and most industrial wastewater treatment facility".

Analysis of polybrominated diphenyl ethers (PBDEs) in sewage sludge after agricultural application. PBDE concentrations in sewage sludge ranged from 197 to 1185 ng/g dry weight (dw).

Earthworms and soil samples were collected from three Midwest agricultural fields in order to analyze them for the presence of 77 anthropogenic waste indicators from land-applied biosolids and livestock manure.

The occurrence of five endocrine-disrupting compounds (EDCs) was tested in the treated wastewater and sewage sludge of eight sewage treatment plants (STPs) in Greece. The analytes were extracted by solid-phase extraction or sonication.

This study analyzed the health status of residents living in Wood County, OH, near farm fields that were allowed to use biosolids. “Results revealed that some reported health-related symptoms were statistically significantly elevated among the exposed residents”.

The plasticizers bis (2-ethylhexyl) phthalate (BEHP), bis (2-ethylhexyl) terephthalate (BEHTP) and bis (2-ethylhexyl) adipate (BEHA) were found in major quantities “in the influents, process streams, treated effluent and solid residues of a large physicochemical treatment plant in Montreal, Canada”. Results obtained indicate that “the treatment plant does not effectively remove plasticizers from the influent and represents a significant source of these compounds and their degradation products in the environment”.

Analysis whether debromination was likely in the field; PBDE congener profiles were tracked from a wastewater treatment plant (sludge) to receiving stream sediments and associated aquatic biota.

This study analyzes “aerosol emission rates produced during the spreading of dewatered class B biosolids onto agricultural land”.

”In this study, the presence, composition, and concentrations of organic wastewater contaminants (OWCs) were determined in solid materials produced during wastewater treatment”. Results indicate the need to better analyze the composition of OWCs in biosolids.

This study examines the peer reviewed literature and official governmental reports for the presence of organic chemicals in the sludge as there are no requirement to test sewage sludges for the presence of organic chemicals in the U.S.

“About 76 percent of a commonly used antimicrobial agent exits sewage-treatment plants as a component of the sludge that's often used as a farm fertilizer”, according to the study used to track the chemical through a plant. These results raise a question to the ultimate fate of the antimicrobial in the environment

Study results indicate that “approximately three-quarters of the mass of TCC disposed of by consumers in the sewer shed of the plant is released into the environment by application of municipal sludge (biosolids) on land used in part for agriculture”.

This study focuses on the presence of a wide range of pharmaceuticals in fresh and marine waters. “…much of the research in the area currently focuses on the removal of pharmaceuticals during sewage treatment processes…”

The purpose of this study was to evaluate if experimental exposure of pregnant sheep to a mixture of environmental chemicals…exerted effects on fetal testis development or function; application of sewage sludge was undertaken so as to maximize exposure of the ewes to its contents”.

”Possible sources of 12 organophosphorus flame retardants and plasticizers, some of which are reported to be toxic to aquatic organisms, were investigated in samples of influents, effluents, and sludge from 11 Swedish sewage treatment plants”.

Adsorption of bisphenol-A, 17b-estradiole and 17a-ethinylestradiole to activate and to inactivated sludge from wastewater treatment plants (WWTPs) was investigated, thus allowing to distinguish between pure adsorption and biosorption.

Wastewater treatment releases pollutants present in industrial and residential discharges. “The recycling of sewage sludge (also known as “biosolids”) as a soil amendment presents additional challenges to the wastewater industry, as they must now also assure these complex materials do not adversely effect the environment”.

This review looks at the effects of land application of contaminated waste products. Toxic metals in sewage sludges applied to agricultural land are used to “illustrate that metal behavior in soils and plant uptake is difficult to generalize because it is strongly dependent on the nature of the metal, sludge, soil properties and crop”.

Purpose of this study was to evaluate different airborne bacterial endotoxin in sewage treatment plants. Results show that “higher values can be recorded during work practises where agitation of wastewater occurs.

“The behavior of fluoroquinolone antibacterial agents (FQs) during mechanical-biological wastewater treatment was studied by mass flow analysis”. The fate of FQs in agricultural soils after sludge application was also investigated.

“The current approach to addressing health and ecosystem risks from biosolids, or sludge, requires identification of so-called “safe” or “acceptable” levels of exposure and installation of controls to achieve such levels.” There is a need to “understand and address risks of biosolids contamination, we present a new, preventative paradigm for addressing the hazards of sludge”.

This study analyzes the impact of pharmaceuticals drugs on the environment. “There is an increased presence of human and animal drugs, including hormones, antibiotics, and antineoplastic compounds in soil, lakes, rivers, and tap water”.

Survey on the “occurrence of pharmaceuticals, hormones, and other organic wastewater contaminants (OWCs) in water resources”. Concentrations of 95 OWCs were measured in water samples from a network of 139 streams across 30 states during 1999 and 2000.

Analysis of fertilization of land with processed sewage sludges, which often contain low levels of pathogens, endotoxins, and small amounts of industrial and household chemicals.

“A method for the quantitative determination of humanuse fluoroquinolone antibacterial agents (FQs) ciprofloxacin and norfloxacin in sewage sludge and sludge-treated soil samples was developed”.

“…potentially hazardous substances, like mercury, solvents, and pharmaceutical compounds, are introduced into the waste stream and ultimately into sewage sludge”.

“…U.S. Geological Survey (USGS) scientists found that biosolids contain relatively high concentrations (hundreds of milligrams per kilogram) of the active ingredients commonly found in a variety of household products and drugs”.

“Spreading sewage sludge on land is but the latest in the compounding of environmental damage from sewerage. This practice must be banned and there must be a federal reorientation of all technology dealing with human excreta and the waste materials from industry and society that now are carried away by sewers”.

High concentrations of several problematic compounds have been detected in biosolids. These results and other findings call into question the EPA’s assessment’s certainty."

The majority of U.S. sewage sludges are disposed by application to land for use as a soil amendment. “…the potential for off-site movement of chemicals, pathogens, and biological agents suggests that their use should be eliminated”.

“Disposal of sewage sludge by application to agricultural and other land is widely practised and is presumed to be environmentally beneficial, but we have found high concentrations of an environmentally persistent class of organic pollutants, brominated diphenyl ethers (BDEs), in ‘biosolids’ from four different regions of the United States”.

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