The accumulation of potentially-toxic metals by grazing ruminants

Risk assessment of four toxic heavy metals in terrestrial and aquatic ecosystems around BSCIC tannery industrial estate of Savar, Dhaka, Bangladesh

The shifting of tannery industries from Hazaribagh to Savar adjacent to Dhaleshwari River might have inevitable adverse impacts, especially the heavy metal contamination of both terrestrial and aquatic ecosystems. The study was carried out to investigate the concentrations of four heavy metals in the soil, water, and plant samples collected from around Dhaleshwari River adjacent to the Bangladesh Small & Cottage Industries Corporation Tannery Industrial Estate, Dhaka. This study revealed that average concentrations of cadmium and chromium in soil exceeded the maximum permissible limit of World Health Organization (1996) and average concentrations of lead, cadmium, and chromium in water exceeded the maximum permissible limit of World Health Organization (2011) and Environmental Conservation Rules (1997). The average concentrations of lead, cadmium, and chromium in the roots and shoots of both Eichhornia crassipes and Cynodon dactylon exceeded the maximum permissible limit of Food and Agriculture Organization/ World Health Organization (2016). Ecological risk assessment using indices model for soil pollution indicated that soil is mostly contaminated with cadmium and chromium which can pose strong ecological risk Health risk assessment using indices model for water pollution revealed the high degree of contamination and unacceptable non-carcinogenic risk and carcinogenic risk for adults as well as children through ingestion of water. Average bioconcentration factor and bioaccumulation factor were higher in Eichhornia crassipes than Cynodon dactylon for lead, cadmium, and chromium. Average translocation factor was also higher in Eichhornia crassipes for all the metals except cadmium. It is suggested remedial and mitigation measures be instituted to control environmental degradation of the newly established Tannery Industrial Estate.

Potentially toxic elements in soil-plant-water-animal continuum in a mining area from Northwestern Mexico: animal exposure pathways and health risks for children

Mining increases environmental concentrations of potentially toxic elements (PTEs) accumulating in organisms and spreading in the human food chain-their presence in milk is of great human health concern. Pathways were identified by which these elements reach raw milk from farms within a mining area in Northwestern Mexico; health risks for dairy cattle and children were also evaluated. Water from river and cattle waterers, as well as, soils showed that PTE concentrations generally below the Mexican and international limits; cattle forage concentrations were above the World Health Organization limits. Al, Mg, Mo, Ni and Zn were recorded in raw milk samples from the mining area, showing that Cd, Co, Cr, Cu, Pb and V are transferred from soil to plants but not accumulated in raw milk. Zn concentrations in raw milk exceeded the permissible limit; milk from farms without mining operations (comparison site) showed the presence of Al, Cr and Cu. In cattle tail hair, PTE did not correlate with raw milk concentrations. Metal accumulation in milk was higher through water consumption than that accumulated through forage consumption. Daily intakes (DI) of Al, Mg and Zn in cows could represent a risk for their health. The observed biotransference was higher than in other parts of Mexico, and the calculated DI and hazard quotients indicate no adverse health effects for children. However, the hazard Index values indicate that exposure to multiple PTE represents a risk for children. Management measures should be performed to control the cumulative risks to protect young children's health.

Accumulation of copper and lead in ruminants grazing on a contaminated shooting range in Nordland County, Norway

Shooting ranges contain copper (Cu) and lead (Pb) contamination, which can be a risk for grazing ruminants. This study examines the accumulation of lead and copper in blood of lambs and calves, as well as in the liver of lambs. It compares these results with those of a previous study, which calculated the ingested dose of copper and lead based on soil ingestion and concentration in soil and plants. Blood samples were collected both before and after the grazing period that lasted from late May to mid-September. Liver samples were obtained during the slaughter of the lambs in the fall. Out of 61 liver samples, only one (3.7 mg Pb/kg dw) exceeding the presumed normal level in lamb liver of 3 mg/kg (dw). Copper concentrations exceeding the normal (300 mg/kg dw) concentration was found in 14 of the liver samples (341-1877 mg Cu/kg dw). Among these, two liver samples (1069 and 1877 mg Cu/kg dw) exceeded the level at which sheep are poisoned (1000 mg/kg dw). There was no statistically significant difference in the copper and lead concentration in liver of lambs that did and did not have the shooting range as part of their pasture. The average concentration of copper (lamb: 1.1 ± 0.37 µg Cu/g, calves: 0.6 ± 0.16 µg Cu/g) and lead (lamb: 0.010 ± 0.008 µg Pb/g calves: 0.01 ± 0.014 µg Pb/g) in the blood samples collected from the lambs and calves did not exceed the upper limit of what is considered normal (sheep: 1.35 mg Cu/kg and 0.3 mg Pb/kg, cattle: 1.7 mg Cu/kg and 0.35 mg Pb/kg). Copper concentration in the blood was notably higher in samples collected from the sheep before (1.3 ± 0.35 µg Cu/g) compared to after (0.8 ± 0.22 µg Cu/g) the grazing period. No statistically significant difference was found in lead and copper concentrations in the blood of lambs and calves grazing inside (lamb: 0.7 ± 0.21 µg Cu/g and 0.01 ± 0.008 µg Pb/g, calves: 0.6 ± 0.16 µg Cu/g and 0.02 ± 0.020 µg Pb/g) and outside (lamb: 0.9 ± 0.21 µg Cu/g and 0.13 ± 0.008 µg Pb/g, calves: 0.6 ± 0.17 µg Cu/g and 0.009 µg Pb/g) the shooting range. Grazing on areas contaminated by shooting activity did not appear to have any major implications for the accumulation of copper and lead in blood of cattle and sheep, as well as in the liver of sheep. The findings from this study indicate that employing site specific risk assessments for ruminants incorporating soil ingestion represents a viable approach.

The effects of soil intake on the growth performance, rumen microbial community and tissue mineral deposition of German Mutton Merino sheep

Soil ingestion by livestock is common in grazing ecosystems, but few studies have been conducted to assess its effect on the animal organism. The topic is worthy of attention because these potential effects are likely to be enriched in the food chain and interfere with animal and human health. In this study, we present an indoor feeding trial conducted based on a completely randomized design to comprehensively evaluate the effects of simulated soil ingestion during grazing on nutrient digestibility, rumen fermentation, and microflora, and mineral deposition in the organs and tissues of sheep. Eighteen Mutton Merino crossbred sheep (42.7 ± 2.34 kg) were randomly allotted to three treatments and fed diets containing 0% (Control), 5% (SOIL5), and 10% (SOIL10) for 62 d, including a 7-d metabolism trial. It was found that soil intake altered the rumen fermentation in sheep, as evidenced by a decrease in total volatile fatty acids (VFA) and acetate concentrations in rumen fluid of 50.6% and 51.3%, respectively (p < 0.01), with soil proportion in the diet increased from 0% to 10%. Soil ingestion also reduced the species richness of rumen bacteria, with the relative abundance of Bacteroidetes decreasing significantly (p < 0.01), while that of Firmicutes and Proteobacteria increased considerably (p < 0.05). In terms of mineral elements deposition, higher levels of iron (Fe) were detected in the spleen and liver, and a higher concentration of copper (Cu) and zinc (Zn) in the liver were found in sheep fed a diet containing 5% soil compared to the other two groups (p < 0.05). Moreover, the concentrations of lead (Pb) in the liver and kidney, and arsenic (As) in the heart were also clearly increased after ingestion of soil (p < 0.05). Our findings indicate that although soil intake had no significant effect on the growth performance of sheep, it altered ruminal fermentation and increased the risk of excessive Fe, Pb, and As in their organism. This study supplies a theoretical basis for risk assessment of soil ingestion in grazing livestock.

Forage accumulation of potentially toxic elements (PTEs) from soils around Kilembe copper mine, Western Uganda

Past copper mining within Kilembe valley between 1956-1982 left behind mine tailings rich in potentially toxic elements (PTEs). This study was conducted to assess the concentrations of PTEs in soils and the potential uptake by forage. Tailings, soils and forage were collected and analyzed using ICP-MS. The study established that over 60% of grazed plots contained high concentrations of Cu, Co, Ni and As. Copper in 35%, Co in 48% and Ni in 58% of forage soil plots exceeded the thresholds for agricultural soils. Bio-accumulation of Zn and Cu, was observed. Zinc in 14% of guinea grass (Panicum maximum), 33% coach grass (Digitalia Scarulum) and in 20% of elephant grasses (Penisetum perpureun) exceeded thresholds of 100-150 mg kg-1. Copper (Cu) concentrations in 20% of Penisetum perpureun and 14% of Digitalia Scarulum exceeded grazing thresholds of 25 mg kg-1. Containment of tailing erosion should be explored to control erosion of tailings into grazing areas.

Impact of Potentially Toxic Compounds in Cow Milk: How Industrial Activities Affect Animal Primary Productions

Potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) frequently coexist in soils near industrial areas and sometimes in environmental compartments directly linked to feed (forage) and food (milk) production. However, the distribution of these pollutants along the dairy farm production chain is unclear. Here, we analyzed soil, forage, and milk samples from 16 livestock farms in Spain: several PTEs and PAHs were quantified. Farms were compared in terms of whether they were close to (<5 km) or far away from (>5 km) industrial areas. The results showed that PTEs and PAHs were enriched in the soils and forages from farms close to industrial areas, but not in the milk. In the soil, the maximum concentrations of PTEs reached 141, 46.1, 3.67, 6.11, and 138 mg kg^-1 for chromium, arsenic, cadmium, mercury, and lead, respectively, while fluoranthene (172.8 µg kg^-1) and benzo(b)fluoranthene (177.4 µg kg^-1) were the most abundant PAHs. Principal component analysis of the soil PTEs suggested common pollution sources for iron, arsenic, and lead. In the forage, the maximum contents of chromium, arsenic, cadmium, mercury, and lead were 32.8, 7.87, 1.31, 0.47, and 7.85 mg kg^-1, respectively. The PAH found in the highest concentration in the feed forage was pyrene (120 µg kg^-1). In the milk, the maximum PTE levels were much lower than in the soil or the feed forages: 74.1, 16.1, 0.12, 0.28, and 2.7 µg kg^-1 for chromium, arsenic, cadmium, mercury, and lead, respectively. Neither of the two milk samples exceeded the 20 µg kg^-1 limit for lead set in EU 1881/2006. Pyrene was the most abundant PAH found in the milk (39.4 µg kg^-1), while high molecular weight PAHs were not detected. For PTEs, the results showed that soil-forage transfer factors were higher than forage-milk ratios. Our results suggest that soils and forages around farms near industries, as well as the milk produced from those farms, have generally low levels of PTE and PAH contaminants.

Comorbidities and concentration of trace elements in livers of European bison from Bieszczady Mountains (Poland)

European bison is a species for which health monitoring is essential in conservation activities. So far, little research has been carried out on the concentration of elements in this species. Most previous studies did not associate the concentration of elements with susceptibility to diseases. In this study we investigate the relationship between comorbidities in European bison and concentrations of a wide spectrum of elements in the liver. Samples were collected during the monitoring of the European bison population in Bieszczady (southeast Poland) over the 2020-2022 period. Each individual was also visually inspected by a veterinarian in the field for the presence of lesions as a part of a post-mortem examination. The animals were divided into 3 groups: group A-one type of clinical sign; group B-two types of clinical signs; group C-three or more types of clinical signs. The ICP-OES method was applied to assess the concentration of 40 elements in livers. Discriminant analysis showed clear differences between the mineral status of individuals in the groups with one, two, and at least three types of clinical signs. Detailed analysis of selected elements showed that, in the case of eight elements, there was a relationship with age, sex, or comorbidities. Cu, Se, and Zn showed significant differences in relation to comorbidities, but only Cu concentration was lower when the frequency of lesions was higher. We concluded that in research on the mineral status of the population, apart from the availability of trace elements in the environment, the health condition of the studied individuals should also be considered. However, inferring the mineral status of the population on the basis of randomly obtained samples from dead individuals may give an incomplete view of the population, especially in the case of species susceptible to diseases, such as European bison.

Phytoremediation potential of Solanum viarum Dunal and functional aspects of their capitate glandular trichomes in lead, cadmium, and zinc detoxification

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg^-1 DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg^-1DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM-EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Cadmium Accumulation in the Goat Liver and Kidney Is Partially Promoted by the Upregulation of Metal Transporter Genes

Metal transporters, including divalent metal-ion transporter-1 (DMT1), Zrt-/Irt-like protein 8 and 14 (ZIP8 and ZIP14), and ferroportin-1 (FPN1), reportedly participate in cellular cadmium (Cd) uptake, but those in farm animals remain unclarified. This study aimed to examine the growth, plasma biochemical indices, Cd accumulation, and expression of metal transporter genes in the liver, kidney, and muscle of goats exposed to rice paddies contaminated with different levels of Cd. Twenty-four goats were randomly assigned across three dietary treatments: 0.23, 0.63, and 1.07 mg of Cd/kg of dry matter (DM) for 60 days. The results showed that dietary Cd exposure increased (p < 0.05) both Cd accumulation and the mRNA expressions of metal transporter genes (DMT1, ZIP, and FPN1) in the liver and kidney but not in the muscle, suggesting dietary Cd exhibited different deposition rates between goat liver, kidney, and muscle. These outcomes suggest that high levels of dietary Cd stimulated the expression of metal transporter genes and thereby enhanced the uptake and accumulation of Cd in the goat liver and kidney. As such, higher Cd concentrations in the liver and kidney observed with Cd diets could be partly explained by upregulation of metal transport genes expression.

Exposure to Copper Compromises the Maturational Competency of Porcine Oocytes by Impairing Mitochondrial Function

Copper (Cu) is an essential trace element for animals, and also an important nutritional component for the normal physiology and metabolism of animal reproductive systems. An excess or lack of Cu will directly or indirectly affect animal reproductive activities. However, the effect of Cu, in particular excessive Cu, on the reproductive performance of sows has not been studied. Here, we report that excessive Cu had negative effects on oocyte maturation and organelle functions. We showed that Cu exposure perturbed porcine oocyte meiotic maturation and impaired spindle/chromosome structure, resulting in a defective spindle assembly, as well as the abnormal distribution of actin dynamics and cortical granules. In addition, single-cell transcriptome analysis identified the target effectors of Cu actions in porcine oocytes, further demonstrating that Cu exposure affects the mitochondrial distribution and function, leading to the high levels of reactive oxygen species, DNA damage, and early apoptosis of porcine oocytes. These findings demonstrate that Cu exposure causes abnormalities in the mitochondrial distribution and function, resulting in the increased oxidative stress and levels of reactive oxygen species, DNA damage, and apoptosis, ultimately leading to a decreased porcine oocyte quality.

Effect of mineral supplementation on lead bioavailability and toxicity biomarkers in sheep exposed to mining pollution

The chronic exposure of livestock to lead (Pb) pollution in historical mining areas may represent significant and unnecessary costs for farmers and primary producers, in addition to important food safety risks. Here, we evaluate the effect of mineral supplements, in the form of a commercial mineral block (MB), to reduce Pb bioavailability and toxicity in sheep through an experimental approach under real farming conditions in an abandoned mining area. Blood, fecal Pb levels, and soil ingestion, along with different blood and plasma biomarkers were studied. Experiment 1 was carried out with 3-months-old female lambs, n = 54, fenced in two contiguous MB and non-MB-supplemented plots. After 20 days of treatment, blood Pb level was lower in MB-supplemented sheep than in those that were non-MB-supplemented. Experiment 2 was carried out with 2-months-old female lambs, n = 34, fenced in a single plot and MB-supplemented during the first 20 days of experiment. After MB supplementation, blood Pb level in sheep was also reduced by almost half, falling below the threshold of subclinical intoxication, and then increased again after 20 days without MB. Experiment 3 was carried out with adult rams, n = 10, fenced in a single MB-supplemented plot during the first 20 days of experiment. In this case, blood Pb level decreased by day 40. Soil ingestion was not reduced by MB supplementation in any of the experiments. MB supplementation favored antioxidant status by increasing SOD activity and reducing GPX activity and MDA levels. In conclusion, the MB supplementation seemed to reduce Pb bioavailability by increasing its fecal excretion, but renal excretion and bone deposition may also have favored the reduction of blood Pb concentration. Mineral supplements may be a new easy-to-apply and cost-effective way to reduce livestock exposure in Pb polluted sites.

A Systematic Framework for Collecting Site-Specific Sampling and Survey Data to Support Analyses of Health Impacts from Land-Based Pollution in Low- and Middle-Income Countries

The rise of small-scale and localized economic activities in low- and middle-income countries (LMICs) has led to increased exposures to contaminants associated with these processes and the potential for resulting adverse health effects in exposed communities. Risk assessment is the process of building models to predict the probability of adverse outcomes based on concentration-response functions and exposure scenarios for individual contaminants, while epidemiology uses statistical methods to explore associations between potential exposures and observed health outcomes. Neither approach by itself is practical or sufficient for evaluating the magnitude of exposures and health impacts associated with land-based pollution in LMICs. Here we propose a more pragmatic framework for designing representative studies, including uniform sampling guidelines and household surveys, that draws from both methodologies to better support community health impact analyses associated with land-based pollution sources in LMICs. Our primary goal is to explicitly link environmental contamination from land-based pollution associated with specific localized economic activities to community exposures and health outcomes at the household level. The proposed framework was applied to the following three types of industries that are now widespread in many LMICs: artisanal scale gold mining (ASGM), used lead-acid battery recycling (ULAB), and small tanning facilities. For each activity, we develop a generalized conceptual site model (CSM) that describes qualitative linkages from chemical releases or discharges, environmental fate and transport mechanisms, exposure pathways and routes, populations at risk, and health outcomes. This upfront information, which is often overlooked, is essential for delineating the contaminant zone of influence in a community and identifying relevant households for study. We also recommend cost-effective methods for use in LMICs related to environmental sampling, biological monitoring, survey questionnaires, and health outcome measurements at contaminated and unexposed reference sites. Future study designs based on this framework will facilitate consistent, comparable, and standardized community exposure, risk, and health impact assessments for land-based pollution in LMICs. The results of these studies can also support economic burden analyses and risk management decision-making around site cleanup, risk mitigation, and public health education.

Essential differences in the mineral status of free-ranging European bison Bison bonasus populations in Poland: The effect of the anthroposphere and lithosphere

Tracking the concentration of elements in the organs of endangered animal species can provide significant knowledge about environmental hazards and allows more targeted protective measures to be taken. In this paper the differences in concentrations of 27 elements in the livers of free-ranging European bison were studied. The ICP-OES method was applied to study the four main Polish populations, which live in lowland (Białowieska, Knyszyńska and Borecka forests) and mountain (Bieszczady) habitats. The study was based on a unique and relatively large amount of comparative material. It was found that European bison populations that live in different locations differ from each other in terms of the hepatic concentrations of 17 of the elements studied in this work. The mountain population in Bieszczady was most distinctive due to the higher concentrations of Ba, Ca, Cd, Se, and the lower concentrations of Mo and V (compared to the other populations). Additionally, even geographically close lowland populations sometimes have different hepatic concentrations of particular elements. The sex and age of individuals have a weak effect on mineral status. Although the lithosphere is the primary factor that affects the availability of elements for the European bison, the soil parameters and biosphere can significantly affect the availability of elements, e.g. by accumulation. It was also shown that the anthroposphere plays a role, but this is mainly through agriculture as feeding on arable fields significantly changes the mineral status of European bison. The need for further research, especially on Cd, Se and Cu, was indicated. It was concluded that toxic elements or deficiencies in essential elements in the populations of the studied species should be considered locally as this would allow better understanding of the health condition of individual populations.

Discrimination of mutton from different sources (regions, feeding patterns and species) by mineral elements in Inner Mongolia, China

The traceability of mineral element fingerprints to mutton in a small area of China was studied. The element data of 104 sheep and 24 goat samples from Inner Mongolia were measured, and the data were analyzed by multivariate statistical analysis from different origins, species and feeding patterns. The results shows that 11 elements (Mg, Al, K, Ca, Mn, Fe, Cu, Zn, Rb, Sr, Ba) in sheep meat had significant differences between different regions (P < 0.05), and the results of linear discriminant analysis (LDA) showed that the accuracy of the original classification rate was 95.2%, and the cross-validation rate was 85.9%. Goat meat and sheep meat samples from Alxa League were also clearly identified with LDA results showing that the cross-validation accuracy of the two species was 70.2%. Then the feeding patterns of sheep meat were effectively classified. The results showed that the multi-element analysis has certain potential as a method to distinguish mutton in a small area.

Cadmium and Lead Exposure, Nephrotoxicity, and Mortality

The present review aims to provide an update on health risks associated with the low-to-moderate levels of environmental cadmium (Cd) and lead (Pb) to which most populations are exposed. Epidemiological studies examining the adverse effects of coexposure to Cd and Pb have shown that Pb may enhance the nephrotoxicity of Cd and vice versa. Herein, the existing tolerable intake levels of Cd and Pb are discussed together with the conventional urinary Cd threshold limit of 5.24 μg/g creatinine. Dietary sources of Cd and Pb and the intake levels reported for average consumers in the U.S., Spain, Korea, Germany and China are summarized. The utility of urine, whole blood, plasma/serum, and erythrocytes to quantify exposure levels of Cd and Pb are discussed. Epidemiological studies that linked one of these measurements to risks of chronic kidney disease (CKD) and mortality from common ailments are reviewed. A Cd intake level of 23.2 μg/day, which is less than half the safe intake stated by the guidelines, may increase the risk of CKD by 73%, and urinary Cd levels one-tenth of the threshold limit, defined by excessive ß₂-microglobulin excretion, were associated with increased risk of CKD, mortality from heart disease, cancer of any site and Alzheimer's disease. These findings indicate that the current tolerable intake of Cd and the conventional urinary Cd threshold limit do not provide adequate health protection. Any excessive Cd excretion is probably indicative of tubular injury. In light of the evolving realization of the interaction between Cd and Pb, actions to minimize environmental exposure to these toxic metals are imperative.

Soil intake in ruminants grazing on heavy-metal contaminated shooting ranges

Shooting ranges contain copper and lead from spent ammunition, this contamination can represent a risk for ruminants grazing there. The present study investigated the intake of copper and lead by sheep and cattle grazing on shooting ranges. Three factors are important for the ingested dose of metals: soil ingestion rate, accumulation of the metals in plants and grazing behavior. Up to 3700 mg Pb/kg dry weight (dw) and 1654 mg Cu/kg (dw) was found in soil and up to 52 mg Pb/kg (dw) and 35 mg Cu/kg (dw) was found in grass. The limit for sensitive land use set by the Norwegian Environment Agency is 60 mg Pb/kg and 100 mg Cu/kg, and the EU limit in fodder is 33.6 mg Pb/kg (dw). Soil ingestion was found by using titanium as a tracer, as titanium is abundant in soil, but not taken up in plants or animals. Low soil ingestion rates (<2%) were found in all investigated areas, including three shooting ranges and one cultivated pasture. There was no correlation between the copper concentration in soil and grass, such a correlation was found for lead. The risk of copper and lead poisoning by ruminants on shooting ranges was assessed based on the copper and lead concentration in the soil and grass, the soil ingestion rate and the grazing behavior. The risk assessment concluded that the calculated dose of copper (chronic sheep: 0.07, cattle: 0.08, acute sheep: 0.7, cattle: 0.8, mg/kg, body weight (bw), day) and lead (chronic sheep: 0.12, cattle: 0.12, acute sheep: 1.2, cattle: 1.2, mg/kg, bw, day) ingested by ruminants was much lower than both the assumed chronic (Cu sheep: 0.26-0.35 cattle: 8, Pb sheep and cattle:6, mg/kg, bw, day) and acute toxic doses (Cu sheep: 20-100, Pb sheep and cattle: 600-800, mg/kg bw) for sheep and cattle.

Assessment of intake of copper and lead by sheep grazing on a shooting range for small arms: a case study

The Norwegian Armed Forces' shooting ranges contain contamination by metals such as lead (Pb) and copper (Cu) and are often used as grazing pastures for livestock. To determine whether the sheep were at risk from grazing at a shooting range in Nord-Trøndelag (the Leksdalen shooting field), a study was conducted wherein the aim was to determine the amount of soil the sheep were eating, the accumulation of Cu and Pb in the livers of lambs grazing on the shooting ranges, and the accumulation of Pb and Cu in the grass. The grazing behavior of the sheep was mapped using GPS tracking and wildlife cameras. Soil, grass, feces, and liver samples were collected. All the samples were analyzed for Pb, Cu, and molybdenum (Mo), and soil and feces were also analyzed for titanium (Ti). Mean concentrations in grass, soil, feces, and liver was 41-7189, 1.3-29, 4-5, and 0.3 mg/kg Pb, respectively, and 42-580, 4.2-11.9, 19-23, and 273 mg/kg Cu, respectively. The soil ingestion rate was calculated using Ti in feces and soil. From these results, the theoretical dose of Cu and Pb ingested by grazing sheep was calculated. The soil ingestion rate was found to be 0.1-0.4%, significantly lower than the soil ingestion rate of 5-30% usually used for sheep. Little or no accumulation of Cu and Pb in the grass was found. There was no difference between the metal concentrations in the washed and unwashed grass. According to the calculated dose, the sheep were at little or no risk of acute or chronic Pb and Cu poisoning from grazing on the Leksdalen shooting range. The analysis of liver samples showed that lambs grazing on the shooting range did not have higher levels of Cu or Pb than lambs grazing elsewhere. None of the lambs had concentrations of Cu or Pb in their livers indicating poisoning.

Metal exposure in cows grazing pasture contaminated by iron industry: Insights from magnetic particles used as tracers

Magnetic particles (MP) emitted by an iron smelter were used to investigate the exposure of cows grazing on a grassland polluted by these MP and by large amounts of potentially toxic elements (PTE). The morphology as well as the chemical composition of the MP separated from cow dung were studied. Large amounts of typical MP were found (1.1 g kg(-1) dry weight) in the cow dung sampled from the exposed site, whereas these particles were absent from the reference unpolluted site. The ingested MP were mainly technogenic magnetic particles (TMP) emitted by the smelter. Considering the MP concentration in the grazed grass on the exposed site, it was concluded that cows absorb the MP not only from the grass but also from the soil surface. The results of a mild acidic leaching of the MP suggested that the particles were possibly submitted to a superficial dissolution in the abomasum, pointing at a potential route of transfer of the PTE originating from the TMP and leading into food chains. TMP were only a small part of the anthropogenic contamination having affected the soil and the dung. However, due to their unequivocal signature, TMP are a powerful tracer of the distribution of PTE in the different compartments constituting the food chains and the ecosystems. Furthermore, the measurement of the particle sizes gave evidence that a noticeable proportion of the MP could enter the respiratory tract.

Transfer of heavy metals through terrestrial food webs: a review

Heavy metals are released into the environment by both anthropogenic and natural sources. Highly reactive and often toxic at low concentrations, they may enter soils and groundwater, bioaccumulate in food webs, and adversely affect biota. Heavy metals also may remain in the environment for years, posing long-term risks to life well after point sources of heavy metal pollution have been removed. In this review, we compile studies of the community-level effects of heavy metal pollution, including heavy metal transfer from soils to plants, microbes, invertebrates, and to both small and large mammals (including humans). Many factors contribute to heavy metal accumulation in animals including behavior, physiology, and diet. Biotic effects of heavy metals are often quite different for essential and non-essential heavy metals, and vary depending on the specific metal involved. They also differ for adapted organisms, including metallophyte plants and heavy metal-tolerant insects, which occur in naturally high-metal habitats (such as serpentine soils) and have adaptations that allow them to tolerate exposure to relatively high concentrations of some heavy metals. Some metallophyte plants are hyperaccumulators of certain heavy metals and new technologies using them to clean metal-contaminated soil (phytoextraction) may offer economically attractive solutions to some metal pollution challenges. These new technologies provide incentive to catalog and protect the unique biodiversity of habitats that have naturally high levels of heavy metals.

Faecal excretion dynamic during subacute oral exposure to different Pb species in Rattus norvegicus

Faecal excretion is a basic means of detoxification upon ingestion of Pb-contaminated feed. In order to determine a time course of Pb elimination after oral exposure to two different forms of this heavy metal (lead acetate vs. phyto-bound Pb), a feeding study was carried out in experimental rats using the Pb phyto-hyperaccumulator Pistia stratiotes as a model diet. The effect of starvation on Pb excretion was further studied in rats that were fed plant material. Twelve Pb doses (7 μg Pb/1 g BW) were administered orally over a 5-week period. Faeces samples were collected 24 and 72 h post-exposure. Inductively coupled plasma optical emission spectrometry and electrothermal absorption spectrometry methods were used for determination of heavy metal concentrations. Up to 53 % of ingested Pb was rapidly eliminated from the exposed rats via faeces within 24 h after exposure. Faecal excretion in exposed rats differed significantly when compared to that of the control group. Fasting before exposure reduced Pb excretion by up to 50 %. Faecal excretions of both examined Pb forms exhibited almost identical patterns. Considerable differences were revealed concerning total excretion levels; lead acetate was excreted in amount greater extent than those of phytobound Pb. Results of our study suggest that Pb forms occurring in the P. stratiotes tissues are absorbed through the gastrointestinal tract to a greater extent than Pb from lead acetate. Therefore, higher portions of ingested Pb can be available for potential accumulation in tissues of exposed subjects.

Metal exposure and accumulation patterns in free-range cows (Bos taurus) in a contaminated natural area: Influence of spatial and social behavior

Possible effects of spatial metal distribution, seasonal-, ecological- and ethological parameters, on the metal exposure of cows were investigated. Therefore the habitat use, vegetation selection and foraging behavior of two free ranging Galloway herds in a metal polluted nature reserve were observed. Metal concentrations in soil, vegetation, hair, blood and feces were measured. Although both herds lived in the same reserve, their metal exposure differed significantly. A high consumption of soft rush by herd 1 during winter for instance was responsible for a large increase in daily Cd intake. The results of this study suggest that the exposure and health risks of large grazers can probably not only be predicted by a general monitoring of soil and vegetation pollution. Also detailed information about the occurring vegetation types, spatial habitat use together with the social- and foraging behavior and diet selection of the species need to be studied.

Deposition of copper, iron, manganese and zinc in the empty body of growing lambs of the breed German Merino Landsheep

A growth experiment with 108 lambs (breed: German Merino Landsheep) was carried out to examine the effect of gender, body weight (BW) and feeding intensity on the deposition of Fe, Zn, Cu and Mn in the empty body (whole animal minus contents of the gastrointestinal tract and bladder). The lambs (50% female and 50% male animals) were fed at three feeding levels ('low', 'medium' and 'high' by varying daily amounts of concentrate and hay) and slaughtered at different final BWs (30, 45 or 55 kg). Six male and six female animals were killed at a BW of 18 kg representing the animals' BW at the beginning of the comparative slaughter experiment. There were significant main effects for the treatments growth rate and final weight on the daily rate of accretion of the trace elements examined. Feeding intensity had a marked influence on the accretion rate for Fe (P < 0.001), Zn (P < 0.001), Cu (P < 0.001) and Mn (P = 0.003). With increasing feeding intensity (low, medium, high) the daily deposition of these trace elements increased (4.4, 5.2, 6.6 mg/day for Fe; 4.9, 5.5, 6.9 mg/day for Zn; 0.20, 0.36, 0.44 mg/day for Cu; 0.14, 0.16, 0.21 mg/day for Mn). Heavier final BW led to increased daily retention of Zn (P < 0.001) and Mn (P = 0.002). Gender had a marked influence only on the accretion rate for Zn (P < 0.001). Ram lambs had a higher daily deposition of this element than female lambs. Related to 1000 g empty body gain, the following concentrations were found for the trace elements examined: Fe 26.1 mg, Zn 30.0 mg, Cu 1.41 mg and Mn 1.04 mg. A feeding influence was given for Zn (P < 0.001) and Cu (P = 0.039). Feeding level low had higher Zn and lower Cu concentrations. Male animals showed less Fe (P < 0.001) and Zn (P = 0.034) per kg empty body gain than females.

Gonad differential proteins revealed with proteomics in oyster (Saccostrea cucullata) using alga as food contaminated with cadmium

As mercury and lead, cadmium (Cd) is one of the highly toxic metals in both the ocean and land environments, but its toxicological mechanism in organisms including human is still unclear because of the complex toxicological pathways in vivo. Here, the alga Chlorella vulgaris were cultivated at room temperature under the stress of cadmium (1 mg L(-1)) to obtain a toxic food, and then the contaminated food were directly supplied to oyster (Saccostrea cucullata) in seawater. After feeding with C. vulgaris contaminated with Cd (C. vulgaris-Cd), the differential proteins in the oyster gonad (OG) were effectively separated and identified with proteomic approaches. Eleven protein spots were observed to be significantly changed in the OG feeding with C. vulgaris-Cd, which seven spots of these differential proteins were down-regulated while four spots were up-regulated. These altered spots were further excised in gels and identified by a combined technique of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/TOF MS) and database searching. A portion of these differential proteins were further proofed by real-time PCR and Western blotting. The results indicate that the major functions of these differential proteins were described as follows: binding, protein translocation, catalysis, regulation of energy metabolism, reproductive function and skeleton structure. These differential proteins in part may effectively provide a few novel biomarkers for the evaluation of Cd pollution level via a food pathway for harming halobios, mammal and human health, and for understanding the complex mechanisms of Cd toxicity in vivo.

Effect of lead in water on the absorption of copper, iron, manganese and zinc by sheep (Ovis aries) infected with sheep tapeworm (Moniezia expansa)

The sheep tapeworm (Moniezia expansa) and its host Ovis aries were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) for their copper, iron, manganese, zinc and lead levels. Element concentrations in cestode parasites were compared to those in various organs (liver, kidney, and muscle) of sheep. Tapeworms in the small intestine of sheep that were administered 2g of Pb(CH(3)COO)(2) per os daily (7 days) had significantly higher lead concentrations than sheep tissues. Cu levels significantly increased after Pb administration in sheep muscle and sheep tapeworms. Contrarily, Zn content significantly decreased in sheep muscle, but significantly increased in sheep tapeworms. However, Mn content significantly decreased after Pb administration in sheep tapeworms. Furthermore, Fe content significantly decreased after Pb administration in sheep liver and kidneys.

A model of cadmium accumulation in the liver and kidney of sheep derived from soil and dietary characteristics

BACKGROUND

Cadmium accumulates in sheep tissues and often approaches the legal limit for human consumption in kidneys. Previous models have focused on transfer from plants to sheep but have restricted value due to seasonal and species variation in plant cadmium concentration. We created a model for the accumulation of cadmium in sheep using empirical relationships previously derived for accumulation in sheep kidney and liver from feeds, together with equations for accumulation in feeds derived from soil characteristics. The combined model relates soil cadmium to liver and kidney concentrations.

RESULTS

Sensitivity analysis demonstrated that the kidney accumulated cadmium faster than the liver and the greatest influence was the total cadmium concentration in the soil. The weight gain of the sheep and soil pH where the feed was grown had relatively minor influences on cadmium concentration in liver or kidney.

CONCLUSION

A combined model of soil, plant and sheep kidney and liver characteristics enables concentrations of cadmium in sheep liver and kidney to be predicted from soil characteristics. This will enable the long-term risks of specific sites to be predicted with greater accuracy than if just plant cadmium concentrations were utilized.

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: II. Metal concentrations in blood and wool

Sheep grazing metal-contaminated floodplain pastures across mid-Wales ingest high concentrations of lead (Pb) in vegetation and directly in the form of soil. Sheep whole blood analysis indicated that Pb concentrations can be significantly elevated for animals grazing contaminated sites: in winter/spring, a median blood concentration of 147 microg Pb l(-1) was found at the location with the highest soil enrichment of this metal compared to only 26 microg Pbl(-1) for the control flock. There was within-flock variability in blood-Pb concentration, and overlap between blood-Pb ranges in animals grazing control and contaminated sites, although use of the Kruskal-Wallis H test established a number of significant (P<0.05) differences between the blood-Pb content of flocks grazing the various study locations. Despite total daily intakes of up to 723 mg Pb d(-1), only one individual sheep showed a blood-Pb content above the 'normal safe' concentration of 250 microg l(-1). Blood and wool analyses were found to have limited value for the diagnosis of environmental exposure to Pb, and further consideration of metal accumulation in offal, bone and muscle tissue is recommended.

Anthropogenic pollutants: a threat to ecosystem sustainability?

Pollutants, including synthetic organic materials and heavy metals, are known to adversely affect physiological systems in all animal species studied to date. While many individual chemicals can perturb normal functions, the combined actions of multiple pollutants are of particular concern because they can exert effects even when each individual chemical is present at concentrations too low to be individually effective. The biological effects of pollutants differ greatly between species reflecting differences in the pattern of exposure, routes of uptake, metabolism following uptake, rates of accumulation and sensitivity of the target organs. Thus, understanding of the effects of pollutants on wildlife and ecosystems will require detailed study of many different species, representing a wide range of taxa. However, such studies can be informed by knowledge obtained in more controlled conditions which may indicate likely mechanisms of action and suitable endpoint measurements. Responses may be exacerbated by interactions between the effects of pollutants and environmental stressors, such as under-nutrition or osmotic stresses and so changes in such variables associated with climatic changes may exacerbate physiological responses to pollutant burdens.

Food chain transfer of cadmium and lead to cattle in a lead-zinc smelter in Guizhou, China

Cadmium (Cd) and Lead (Pb) are environmental pollutants. Environmental samples and bovine tissues were collected from the areas around a lead-zinc smelter in Guizhou, China for Cd, Pb, zinc (Zn) and copper (Cu) analysis. Cd in soil (10 mg/kg) and feed (6.6 mg/kg) from the polluted areas was 10 times higher than the Chinese Standards, resulting in higher Cd in bovine kidney (38 mg/kg) and liver (2.5 mg/kg). Pb in feed (132 mg/kg) from the polluted area was much higher than unpolluted areas, causing higher Pb levels in bovine tissues. Environmental Zn was elevated, but bovine tissue Zn was normal. Cu in bovine liver decreased with increased Cd and Pb. Metals in drinking water and in bovine muscle were within the Standard range. Thus, in the areas of this lead-zinc smelter, the environment has been contaminated with Cd and Pb, which has been transferred to cattle through the food chain.

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: I. Soil ingestion, soil-metal partitioning and potential availability to pasture herbage and livestock

This paper first evaluates the relative importance of the soil-plant-animal and soil-animal pathways of Zn, Cu and (especially) Pb investigated over a 15-month study period at 12 floodplain sites located within and downstream of the mineralised and historic mining area of mid-Wales, and secondly considers the implications of a sequential extraction procedure (SEP) undertaken on soils of varying particle size sampled from the study locations. Generally, very good agreement was found between the chemical partitioning of the three metals for each of the physical soil fractions subjected to the SEP. The availability of Pb to pasture vegetation, especially at the contaminated sites, is indicated with its associations with the more soluble (i.e. exchangeable and Fe/Mn oxide) soil phases, yet soil and/or plant barriers effectively restrict above-ground herbage concentrations of this metal. Consequently, with sheep ingesting soil at rates varying according to season from 0.1% to 44% or more of dry matter intake, the soil-animal pathway accounts for the majority of Pb consumption through most of the year, and at moderately and highly contaminated sites significant quantities of relatively soluble soil-Pb can be ingested at rates exceeding safety threshold limits.

Evaluation of pastures for horses grazing on soils polluted by trace elements

Pasture established on polluted soil may pose a risk to grazing livestock creating a requirement for mechanical management which may affect biodiversity and expend energy. The risk associated with managing pasture by grazing horses (non-edible livestock) is being assessed in the Guadiamar Valley (SW Spain), where soils are polluted with trace elements following a major pollution incident. Soil pollution does not affect biomass production or floristic composition of pasture, although both variables influence trace element accumulation in herbage. Element concentrations in herbage are below maximum tolerable limits for horses. Faecal analysis showed regulated absorption of essential elements, while non-essential elements seemed preferentially excreted. Elemental content of horse hair did not differ in animals from polluted and control pastures. If pastures are managed by grazing, periodic monitoring is recommended in view of the long-term chronic trace element exposure in these systems.

Metal accumulation in cattle raised in a serpentine-soil area: relationship between metal concentrations in soil, forage and animal tissues

Soils developed on serpentine rocks contain high levels of heavy metals such as copper (Cu), nickel (Ni) and chromium (Cr), and are deficient in some macronutrients. The crops and pasture grown on these soils may accumulate high levels of metals, which constitute a potential health hazard for cattle. The aim of this study was to evaluate Cr, Ni and Cu accumulation in cattle raised in a serpentine area in Southwest Europe (Galicia, NW Spain). Samples of liver, kidney and muscle of 41 animals aged 8-12 months were collected at slaughter. Representative samples of soil and forage were taken from 10 farms. Samples were acid-digested and metal concentrations determined by ICP-MS (Cr and Ni) and ICP-AES (Cu). The concentrations of the metals in soils and forage were in the range of those found in serpentine soils in other areas. Accumulation of Cr in animal tissues was generally low and within the normal range. However, 20% of the animals had toxic levels of Ni in kidney and 32% of the animals had liver Cu levels above the acceptable range. Serpentine soils had a significant effect on Ni and Cu accumulation in cattle, and a relatively high percentage of the animals showed tissue levels of Ni and Cu indicative of risk of toxicity.

Endocrine disruptors and other food-contaminating environmental pollutants as risk factors in animal reproduction

Pollutants of many chemical classes, derived primarily from anthropogenic activities, are ubiquitous in the environment, persistent, biologically available and can exert adverse effects on the reproductive and other, indirectly related, physiological systems. Food is generally considered to be the major route of animal exposure in vertebrate species but the relative contributions of other routes of exposure such as through lungs, gills or skin are not well studied and may be of importance for certain animal groups, depending on their immediate environment. Animals are particularly sensitive to exposure during developmental stages but the pattern of exposure to chemicals is likely to be different to that of adults. Quantification of the risk posed by the ingestion of pollutants in food is complex and depends on many factors including species, diet composition, duration of exposure to the food, efficiency of pollutant absorption, subsequent metabolism, sensitivity of target organs and stage of development. While the effects of high doses of single chemicals are proven, dietary exposure to pollutants generally involves prolonged, low-level exposure to a large number of compounds, each of which has different chemical characteristics, exerts different biological effects and is present at varying concentrations. Thus, while exposure to pollutants through feed is undoubtedly a significant risk factor for many species and may be the most important one for many terrestrial vertebrates, other routes of exposure may be more important in other groups.

Accumulation of potentially toxic metals in the liver tissue of sheep grazed on sewage sludge-treated pastures

Concentrations of potentially toxic metals (PTMs) in the livers of pregnant, mature ewes and their 110 day foetuses, and in 6-month old lambs born to other ewes, were determined. The animals had been reared on pastures fertilized for 5 years with either sewage sludge (treated; T) or conventional inorganic fertilizer (control; C). The effects of treatment on patterns of accumulation of PTMs differed with stage of development and with individual PTM. In the liver of lambs, concentrations of Pb were elevated in T compared with C liver (P < 0·01), while Cu and Zn were lower (P < 0·001) in T than C liver. By contrast, in ewe liver, Cu concentrations were lower in T than C liver (P < 0·05), as in lambs, but there were no other treatment differences in PTM concentration. Ewe and lamb tissue data were not directly comparable because they were exposed to different diets but mean concentrations of Cd, Ni and Pb were approximately two- to four-fold higher in ewe than lamb liver while mean Cu concentrations were approximately five-fold lower, suggesting that more prolonged exposure to PTMs may have enhanced treatment differences in tissue PTM concentrations. Mean foetal PTM concentrations were not significantly affected by treatment. It is concluded that the repeated application of sludge to pasture is associated with altered, but not necessarily increased, rates of accumulation of PTMs in liver tissue, that rates of accumulation depend on the individual PTM measured and that they are probably influenced by duration and route of exposure and source of nutrient. Limited observations suggested that there was little effect of year, and associated variation in climatic conditions and herbage growth, on PTM accumulation.

Application of cattle manure as fertilizer in pastureland: estimating the incremental risk due to metal accumulation employing a multicompartment model

Specific-site data of metal concentration in cattle manure from NW Spain and a multicompartment fate and exposure model were used to evaluate metal fate and the main routes of exposure after a 100 year period of application of cattle manure as fertiliser in pastureland. Risk assessment was performed as a probabilistic analysis, and using a conservative worst-case exposure scenario. An accumulation model was used to predict the metal concentration in each environmental medium of concern. The incremental risk was estimated for the population inhabiting the surroundings of the area by a general multiexposure model. Monte Carlo simulations were performed to analyse uncertainty of the results. Furthermore, a sensitivity analysis was carried out to identify the contribution to variance by the different metals and exposure routes. Among the five pathways evaluated, the ingestion of meat and milk from cattle grazing in the area represents the main contribution to total exposure. The results indicate that the incremental risk to human health for people living in the surroundings of pasturelands due to continuous application of cattle manure after a 100 year period are not negligible for the metals considered (Cd, Cu, Ni, Pb and Zn), posing a total Reasonable Maximum Exposure (RME) of 0.75, being the ingestion of meat the main exposure pathway.

Effects of cadmium in herbage on the apparent absorption of elements by sheep in comparison with inorganic cadmium added to their diet

A meta-analysis of existing scientific literature recently suggested that Cd is absorbed more efficiently by sheep if it is in the organic form in grass, than if it is added as an inorganic supplement to the diet. We tested this experimentally by feeding sheep grass from contaminated soil, compared with uncontaminated grass and with Cd added to the diet. To produce contaminated herbage, Cd nitrate was added to soil in 11 lysimeters sown with perennial ryegrass, with a further 11 lysimeters receiving no Cd to produce uncontaminated herbage. In the Cd-treated lysimeters, soil had increased exchangeable K, Mg, and Ca, leachate had increased K, Mg, Ca, Na, and P, grass had increased Cd and reduced Mg, Na, P, Mn, Fe, Cr, Al, and Ni, and there was some reduction in grass yield compared with untreated lysimeters. Grass from Cd-treated or untreated lysimeters was fed to groups of 12 ewes for 2 days, with Cd intake equated by adding Cd nitrate to the concentrate feed of ewes receiving the uncontaminated grass. The apparent absorption of Cd, Zn, Mo, Cr, and Al was increased for ewes receiving Cd-enriched grass, and apparent absorption of Cu was reduced, compared to those receiving supplementary inorganic Cd. Most of the unabsorbed Cd was excreted in feces within 4 days of feeding. The ewes consuming Cd in grass had increased B concentrations in their urine, possibly due to adverse effects of Cd on kidney function. Finally, the ewes were offered a choice of the two herbages and they ate significantly more of the uncontaminated grass. It is concluded that the apparent absorption of Cd and other heavy metals by sheep in a short-term experiment was greater when Cd was in the grass than when the Cd was added in in an inorganic form and that sheep partially avoided herbage with a high Cd concentration.

Recycling biosolids to pasture-based animal production systems in Australia: a review of evidence on the control of potentially toxic metals and persistent organic compounds recycled to agricultural land

Biosolids from municipal waste water treatment are commonly used in agriculture as a source of nutrients, organic matter, and irrigation. There is, however, concern that the use of biosolids on pasture can lead to an accumulation of potentially toxic metals (PTM) and persistent organic compounds (POC) in the surface layers of soil and associated herbage that can be ingested by grazing livestock. This review examines the following two key questions. Is the use of these materials in an agricultural setting safe and practical? Is the use of biosolids safe in all climates, on all soils, and is it sustainable over the long term? To answer these important questions, the Australian regulatory framework is examined in light of similar legislation in Europe and the United States on the basis of scientific evidence that underpins the published limits, contaminant gradings, annual loadings, and prescribed restrictions on the use of biosolids in agriculture. The review concludes that the regulatory frameworks currently enacted at State level suffer from a lack of data to underpin the risk assessments conducted to prevent transfer of PTM and POC to the human food chain from livestock production and the basis of published thresholds is poorly defined. The important areas of future research are identified as studies on acquisition and transfer of PTM and POC to grazing animals and the subsequent effect of attenuation of the pollutant on the human food chain, the validation and acceptance of methods to quantify POC in biosolids, the effect of recycling of biosolids on the economic performance of pasture-based agriculture, and the market perception of animal products produced from land receiving biosolids.