The team, led by Aamir Manzoor of PMAS-Arid Agriculture University in Rawalpindi, Pakistan, together with colleagues in Germany, measured zinc, copper, iron, manganese, nickel, chromium, cadmium and lead across blends ranging from pure poultry litter to mixtures dominated by vegetable waste. Because composting shrinks the pile, mostly by driving off water and oxidizing carbon, the concentration of any non-volatile metal should rise roughly in proportion to the loss of dry mass. That simple expectation is the backbone of most interpretations of metal data from composting studies, and it is precisely the assumption the authors set out to stress-test.

The headline result is striking. In the pure poultry litter compost, cadmium rose from 0.84 to 3.34 milligrams per kilogram of dry matter over the 90 days, a fourfold increase. Cadmium is not a contaminant regulators treat lightly: the European Union’s limit for cadmium in organic soil improvers is 2 milligrams per kilogram of dry matter, and by day 90 the two most poultry-litter-rich blends in the trial exceeded it. For a waste stream as widely available as poultry litter, which farms across the world compost in enormous volumes, that is a compliance problem hiding in plain sight.

What makes the finding scientifically interesting, and methodologically uncomfortable, is that the increases in cadmium, chromium and lead could not be reconciled with plausible dry-matter loss alone. The researchers analyzed their data under three different assumptions about how much dry matter the piles had lost, and then used zinc and manganese, two metals whose behavior is comparatively well understood, to infer the most likely loss. After that correction, the mean apparent recovery factors, the ratio of measured to expected metal mass, came out at about 1.03 for zinc, copper, manganese and nickel, which is reassuringly close to the value of one that a closed mass balance would predict. For chromium, cadmium and lead, however, the mean apparent recovery factor was 5.11, with a 95 percent bootstrap interval running from 3.05 to 8.23.

Those numbers demand attention. A recovery factor of five means that, on paper, five times more of these metals appeared at the end of composting than could be accounted for at the start, even after adjusting for mass loss. The authors tested whether extreme assumptions could rescue the mass balance: even if they assumed that half of the pile’s dry matter had vanished, the recovery factors for chromium, cadmium and lead remained above one. In other words, no reasonable amount of shrinkage explains the pattern. Something else was adding apparent metal mass, or the analytical method was recovering more of it than expected.

One candidate is soil. Composting operations inevitably incorporate small amounts of dirt, whether from the pad, the machinery or the turning process, and soil carries its own metal load. The researchers used the increase in iron, a conservative tracer abundant in mineral matter, to estimate how much soil might have entered the piles. The answer was about 0.13 percent mineral addition, a plausible figure. But under simplified mixing assumptions, that soil input could account for only about 4 percent of the chromium increase and less than 1 percent of the lead increase. Soil contamination, in short, is a footnote to the story, not the explanation.

The authors also fitted first-order kinetic models to the concentration changes, obtaining a mean rate constant of 0.0143 per day, which corresponds to a half-time of about 49 days. That is a useful practical number: it tells compost operators that whatever process drives these apparent metal increases, roughly half of the total change occurs within about seven weeks, meaning that mid-process samples can look dramatically different from finished-product samples. It also means that the timing of compliance sampling matters enormously, a point with direct regulatory consequences.

The most provocative interpretation, which the authors raise but carefully refuse to confirm, involves the digestion method itself. To measure total metal content, laboratories digest compost samples in strong acid, and the fraction of metal actually released into solution, the analytical recovery, is rarely perfect and rarely checked. If digestion recovery improved over the course of the experiment, perhaps because the compost matrix became easier to attack as organic matter stabilized, the measured concentrations would rise even if the true metal mass never changed. The authors are explicit that increasing digestion recovery could explain the observed patterns, but that unmeasured dry-matter loss, unquantified metal transfers within the pile, and unknown analytical accuracy prevent them from confirming that mechanism or asserting that metal mass was conserved. The honest conclusion is that the data cannot distinguish between real metal enrichment and an analytical artifact, and that this ambiguity is itself the finding.

The regulatory implications are where the study lands hardest. Compliance testing for compost typically relies on samples taken at a specified point, and the results are compared against fixed limits such as the EU’s 2 milligram per kilogram cadmium threshold for organic soil improvers. The researchers built an uncertainty model around their data and estimated that the probability of exceeding the cadmium limit reaches 5 percent at approximately 48 percent poultry litter in the feedstock blend. That means a producer blending roughly equal parts litter and vegetable waste is already skating near the edge of non-compliance, and the outcome of a single compliance sample could hinge on when it was taken, how much dry matter had been lost, and how well the laboratory’s digestion method performed that week.

From these results the authors draw three practical recommendations, each of which challenges common practice. First, sample the finished product rather than the feedstock or the mid-process pile, because concentrations change most in the later stages and early samples give a misleading picture of what will actually be sold or spread. Second, assess compost maturity independently of metal analysis, since maturity drives both the physical behavior of the material and, plausibly, the performance of the digestion chemistry. Third, validate the digestion method itself, ideally with certified reference materials, so that apparent recovery factors can be interpreted with confidence rather than guessed at. None of these steps is exotic or expensive, yet the study makes clear that their absence can turn a routine compliance check into an exercise in uncertainty.

There is also a broader lesson for environmental monitoring here, one that extends well beyond compost. Concentration data are seductive because they are simple: one number, one limit, one pass or fail. But a concentration is a ratio, with metal mass in the numerator and dry matter in the denominator, and both terms can move during a biological process like composting. When the denominator shrinks, concentrations rise even if nothing has been added; when the analytical method recovers more of the metal, concentrations rise even if nothing has changed at all. The study’s careful separation of these effects, using bootstrap intervals and Monte Carlo analysis to propagate the uncertainty, offers a template for how monitoring programs in other domains, from sewage sludge to biosolids to recycled fertilizers, could be made more honest about what their numbers actually mean.

For the composting industry, the immediate takeaway is caution rather than alarm. Poultry litter remains a valuable and recyclable resource, and the metals at issue were present at modest absolute levels in most blends. But the finding that cadmium can cross a legal limit in litter-rich composts, and that the apparent increases in chromium, cadmium and lead resist explanation by mass balance, should prompt producers and regulators alike to look harder at sampling design and laboratory quality control. In a market that increasingly prizes verified, circular products, the credibility of a compost certificate may depend less on the metal concentrations it reports than on the rigor of the process that produced those numbers.

Subject of Research: Trace metal concentration changes and analytical recovery uncertainty during poultry litter and vegetable waste co-composting

Article Title: Cd, Cr, and Pb concentrations increase during composting: implications of uncertain mass balance and analytical recovery for compliance sampling

Article References: Manzoor, A., Manzoor, M., Aamir, A., Alam, T., & Chaudhry, A. N. (2026). Cd, Cr, and Pb concentrations increase during composting: implications of uncertain mass balance and analytical recovery for compliance sampling. Environmental Monitoring and Assessment, 198(11), Article 1152. https://doi.org/10.1007/s10661-026-15976-w

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15976-w

Keywords: composting, heavy metals, cadmium, chromium, lead, poultry litter, mass balance, analytical recovery, compliance monitoring, organic soil improvers, digestion method, uncertainty analysis

The study set out to answer a deceptively simple question: what does poultry farming actually do to the microscopic life in soil? The researchers collected composite soil samples from two farms within a poultry estate in Ikorodu, designated PF01A and PF02B, and compared them with soil from a pristine control site, labeled CTR, that had no history of farming activity. Using a soil auger, they sampled five points at each location, sieved the material to create composite samples, and transported everything at four degrees Celsius to the laboratory. Ethical and social approvals were secured from the Nigerian Institute of Medical Research and the Lagos State Ministry of Health before any sampling began.

The technical backbone of the study was metagenomic analysis of the bacterial 16S rRNA gene, specifically the V3 to V4 hypervariable regions, which act like molecular barcodes for identifying bacterial taxa. The team extracted total community DNA from half a gram of soil using a commercial soil kit, adding skim milk to the lysis matrix to prevent humic substances from interfering with the polymerase chain reaction. Sequencing was performed on an Illumina MiSeq platform, generating tens of millions of reads that were then quality filtered, merged, denoised, and clustered into operational taxonomic units, or OTUs, using a pipeline that included Trimmomatic, PANDAseq, DUDE-Seq, and UCHIME, with taxonomic assignments made against the EzBioCloud 16S database at a 97 percent similarity threshold.

The scale of the data was considerable. After quality filtering, the researchers obtained 17,714 valid bacterial reads from PF02B, 16,975 from PF01A, and 24,218 from the control site. The farm soils clustered into roughly 1,000 to 1,200 OTUs each, while the pristine soil contained 3,037 OTUs, indicating a far richer and more diverse native community. Good’s library coverage estimates exceeded 98 percent for both farm samples and reached 96 percent for the control, meaning the sequencing captured nearly the entire bacterial community at each site. Alpha diversity indices, including the Shannon and inverse Simpson measures, showed that PF01A hosted greater bacterial diversity than PF02B, but both were dramatically simplified compared with the untouched soil.

The most striking finding emerged at the phylum level. In the poultry-impacted soils, Firmicutes dominated overwhelmingly, accounting for 55 to 69 percent of reads, followed by Bacteroidetes at 18 to 19 percent and Actinobacteria at 3 to 17 percent, while Proteobacteria languished at around 7 percent. The control soil told the opposite story: Proteobacteria led at 30 percent, with Firmicutes at 28 percent, Actinobacteria at 22 percent, and a suite of other phyla, including Acidobacteria, Verrucomicrobia, Chloroflexi, Gemmatimonadetes, and Nitrospirae, each contributing smaller shares. Bacteroidetes, a dominant group in the farm soils, barely registered at 2 percent in the pristine site. This inversion matters because Proteobacteria dominance is the expected pattern in healthy, nutrient-rich soils, so its displacement by Firmicutes and Bacteroidetes is a clear fingerprint of poultry litter.

The explanation, the researchers argue, lies in the origin of the litter itself. Firmicutes and Bacteroidetes are the dominant phyla in the duodenum, ileum, and cecum of chickens, so soil repeatedly receiving poultry droppings is essentially being inoculated with the gut microbiome of the birds. The authors note that the chicken gut microbiota is not stable and shifts with the age of the flock, which suggests the community profile observed in the soil may partly reflect the age of the birds that produced the litter. At the family level, the pattern held: Lactobacillaceae dominated both farm soils at 34.1 percent and 20.4 percent respectively, alongside Bacteroidaceae, Lachnospiraceae, Enterococcaceae, Corynebacteriaceae, Peptoniphilaceae, Planococcaceae, and Ruminococcaceae, while the control soil was led by Bacillaceae, Bradyrhizobiaceae, Gaiellaceae, and Sphingomonadaceae. None of the dominant families in the farm soils exceeded 1 percent abundance in the pristine soil, and heat map analysis confirmed that the two farm samples clustered together, clearly separated from the control.

Within those dominant taxa were species that give public health officials reason for concern. Corynebacterium xerosis, a bacterium implicated in ear infections, osteomyelitis, ventriculoperitoneal shunt infections, and brain abscesses, was among the dominant strains in both farm soils. So was Ignatzschineria indica, a Gram-negative bacillus associated with the parasitic flesh fly Wohlfahrtia magnifica and reported as a cause of bacteremia in patients with maggot-infested wounds. Its presence in poultry-litter soil is unsurprising, the authors note, because the odor of litter attracts swarms of flies. Other dominant organisms included Jeotgalibaca arthritidis, Lysinibacillus jejuensis, and the species Enterococcus lemanii and Enterococcus eurekensis, along with Acinetobacter towneri, a non-baumannii Acinetobacter that, while not typically pathogenic itself, is considered a public health threat because it can accumulate clinically relevant antimicrobial resistance genes potentially transferable to Acinetobacter baumannii, a notorious cause of hospital infections.

The findings sit within a broader and increasingly alarming literature on antimicrobial resistance spreading from livestock into the environment. Untreated poultry litter is a known reservoir of foodborne pathogens such as Campylobacter species, Listeria monocytogenes, Staphylococcus aureus, and Salmonella species, alongside antibiotic residues. In Cameroon, 100 percent of Escherichia coli and 36.4 percent of Salmonella isolates from chicken litter manure were found to be multidrug resistant, and some resistant bacteria carry plasmids that enable horizontal gene transfer, amplifying the spread of resistance genes. In South Africa, 56 percent of Enterococcus species isolated from agricultural soils following chicken litter application were resistant to at least one antibiotic, prompting calls to rethink manure use altogether. Enterococci, which dominated the Lagos farm soils, are notorious for developing resistance to critically important antibiotics.

Not everything in the altered microbiome is bad news. Lactobacillus species, the most abundant family in the farm soils, play a beneficial role in cycling nitrogen-containing compounds such as ammonia in poultry manure, potentially creating a safer environment for both birds and humans. Poultry litter is also a genuine organic fertilizer, supplying nitrogen, phosphorus, and potassium that boost crop growth and stimulate nitrifying bacteria. But the benefits come with well-documented environmental costs: excess phosphates from litter-amended fields can run off into water bodies and drive eutrophication, while nitrate leaching into groundwater has been reported in amended croplands. In neighboring Benin, documented cases of food poisoning from Campylobacter jejuni and Campylobacter coli were linked to leafy vegetables grown with poultry manure, illustrating how the practice can transmit pathogens directly into the food chain.

The Lagos team is careful about the limits of its work. The study covered only two farms and a single control site, a cross-sectional snapshot that may not capture the full dynamics of soil microbial change across larger scales or over time. Still, the researchers argue the data provide a crucial baseline for Nigeria, where livestock farming is economically vital but where, until now, there has been little molecular data on how poultry litter shapes soil microbiomes. Their conclusion is pragmatic rather than alarmist: poultry farming sustains income and nutrition for millions of households, so the answer is not to abandon litter as fertilizer but to treat it before it reaches the soil. The authors point to drying as a practical technology for reducing litter pollution, and they urge that untreated litter no longer be disposed of indiscriminately into pristine environments. As sequencing tools make it ever cheaper to read the microbial state of the ground beneath our feet, the message from Ikorodu is clear: what we spread on the land comes back to shape the invisible ecosystems that underpin soil health, food safety, and human health alike.

Subject of Research: The impact of poultry farming practices on soil bacterial community structure and composition in Lagos, Nigeria

Article Title: Contribution of poultry farm practice to the structure and composition of bacterial communities in the soil of poultry farms in Lagos, Nigeria

Article References: Contribution of poultry farm practice to the structure and composition of bacterial communities in the soil of poultry farms in Lagos, Nigeria. (n.d.). https://doi.org/10.1186/s44329-024-00015-1

Image Credits: AI Generated

DOI: 10.1186/s44329-024-00015-1

Keywords: poultry farming, soil microbiome, 16S rRNA sequencing, Firmicutes, Bacteroidetes, poultry litter, antimicrobial resistance, pathogenic bacteria, Nigeria, public health, metagenomics, soil health

Organic and sustainable farming operations increasingly depend on biological soil amendments of animal origin to build soil health, improve nutrient availability, and sustain crop productivity without relying on synthetic fertilizers. Poultry litter, a mixture of manure, bedding material, feathers, and feed residues, is one of the most abundant and widely used of these amendments. In Georgia, one of the nation’s leading poultry-producing states, approximately two million tons of poultry litter are generated annually, making it an economically and agronomically important resource for vegetable growers across the state. Sweet onions, a signature Georgia crop, are frequently grown in soils amended with these materials.

The research team, which included Harsimran Kaur Kapoor of the University of Georgia and Abhinav Mishra of the university’s Department of Food Science & Technology, set out to answer a deceptively simple question: how long does E. coli remain viable in field soils treated with different poultry litter-based amendments, and how do environmental conditions modulate that survival? The answer matters because pathogenic strains of E. coli and related foodborne pathogens can persist on produce surfaces and within soil ecosystems long after the amendment is applied, creating a window of potential contamination that growers must manage.

Across two growing seasons, the researchers observed a consistent pattern. Soils amended with heat-treated poultry pellets and soils amended with composted poultry litter both supported longer survival of E. coli than untreated control soils. Heat treatment and composting are both intended to reduce pathogen loads in manure-based products, yet the study indicates that the amended soil environment itself, even when the amendment has been processed, can create conditions more favorable to bacterial persistence than unamended soil. Nutrient availability, moisture retention, and organic matter content are among the factors that researchers generally associate with improved microbial survival in amended soils, and the study’s results align with that broader understanding.

The weather findings add a layer of complexity that the authors argue is essential for risk management. The influence of weather differed between the two growing seasons analyzed, pointing to the importance of year-to-year variability. Higher humidity was associated with greater bacterial survival, while stronger winds generally reduced survival. Rain and warmer soil temperatures could promote bacterial persistence, whereas higher air temperature and wind speeds tended to reduce it. Taken together, the results suggest that extreme weather events, rather than average seasonal conditions alone, may play an important role in determining how long bacteria can survive in agricultural soils.

This distinction between averages and extremes carries real consequences for how food safety risk is modeled and managed. A season with a modest average temperature but several intense rainfall events may pose a different contamination profile than a season with a higher average temperature and steady winds. Risk-based approaches that rely solely on seasonal or monthly climate summaries could therefore underestimate the survival window of pathogens following specific extreme events. The authors note that understanding how amendment practices interact with extreme weather may help inform risk-based management approaches under real field conditions, where growers cannot control the weather but can adjust amendment type, timing, and application practices.

The crop at the center of the study is not an arbitrary choice. Onions have been linked to several major foodborne illness outbreaks in North America in recent years. In 2024, the U.S. Food and Drug Administration investigated an outbreak of E. coli O157:H7 associated with slivered onions served on McDonald’s Quarter Pounder burgers. Earlier incidents include a 2020 outbreak of Salmonella Newport linked to red onions across the United States and Canada, and a 2021 outbreak of Salmonella Oranienburg tied to whole fresh onions imported from Mexico. These outbreaks resulted in thousands of reported illnesses and hundreds of hospitalizations, underscoring that allium crops, long considered lower risk than leafy greens, can serve as vectors for serious foodborne disease.

Sweet onions present particular production considerations. They are typically grown in sandy soils with careful irrigation management, harvested after months in direct contact with the soil environment, and often consumed raw or with minimal processing, which means no kill step intervenes between field and consumer. Any pathogen that persists in the soil or on the bulb surface at harvest therefore represents a direct route into the food supply. Understanding whether and how poultry litter amendments extend the survival window of E. coli in these soils gives growers and regulators a concrete variable to work with when designing pre-harvest intervals, amendment application schedules, and water and soil testing regimes.

The regulatory context is also evolving. The authors note that regulators continue to seek data on the food safety implications of biological soil amendments of animal origin, a category that includes raw and processed manures, composts, and pelleted products. Field-scale studies like this one provide the kind of empirical evidence needed to calibrate standards that are both protective of public health and workable for growers who depend on these amendments for soil fertility. The interaction between amendment type and local environmental conditions that the study documents suggests that a one-size-fits-all national standard may be less effective than frameworks that account for regional climate, weather variability, and dominant amendment practices.

For Georgia’s sweet onion industry, and for produce growers in poultry-heavy regions more broadly, the study offers a practical takeaway: the combination of amendment choice and weather exposure deserves active attention in food safety planning. Growers who apply heat-treated poultry pellets or composted poultry litter may want to consider how upcoming rainfall, humidity, and wind patterns could extend or shorten pathogen survival in their fields. As extreme weather events become more frequent and more intense, the researchers’ central finding, that it is the extremes rather than the averages that shape bacterial persistence, is likely to grow in importance for anyone working at the intersection of soil health, agricultural productivity, and the safety of the fresh produce that reaches consumers’ tables.

Subject of Research: Survival of E. coli in poultry litter-amended soils under varying weather conditions in sweet onion production

Article Title: Study finds poultry litter-based soil amendments and weather influence E. coli survival in Georgia sweet onion production systems

Article References: Study finds poultry litter-based soil amendments and weather influence E. coli survival in Georgia sweet onion production systems. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: E. coli, poultry litter, soil amendments, sweet onions, food safety, extreme weather, Georgia agriculture, Risk Analysis, compost, foodborne illness, pathogen survival, produce safety