Parameter values to model the soil ingestion pathway

Dynamics of soil ingestion by growing bulls during grazing on a high sward height in the French West Indies

Free-range livestock are exposed to environmental contaminants by ingesting contaminated matrices mainly soil. Several works evaluated precisely the soil ingestion and its variation factors in ruminants. Contrary to temperate grazing systems, tropical ones were poorly documented whereas weather or traditional grazing practices may change models established in temperate systems. The study was performed in the French West Indies, which are concerned by a widespread environmental chlordecone contamination. The work evaluated daily soil and grass ingestions by tethered growing bulls grazing on a very high sward close to 50 cm for 11 days without being moved. This grazing management is representative to local practices by small farmers or not professional holders and allows completing the results previously obtained. Daily soil ingestion did not significantly increase across time and was on average 26.9 g dry matter/100 kg body weight (i.e. 1.4% of the total mass ingested). Marked individual variations indicated that exposure risk assessments would require experimental designs based on a sufficient number of individuals. This study was also the first to investigate the changes in sward soiling with respect to the distance from the stake and reported lower soil loading on grass in the peripheral than central and intermediate areas.

Assessment of health risks due to arsenic from iron ore lumps in a beach setting

In 2011, an artificial hook-shaped peninsula of 128ha beach area was created along the Dutch coast, containing thousands of iron ore lumps, which include arsenic from natural origin. Elemental arsenic and inorganic arsenic induce a range of toxicological effects and has been classified as proven human carcinogens. The combination of easy access to the beach and the presence of arsenic raised concern about possible human health effects by the local authorities. The objective of this study is therefore to investigate human health risks from the presence of arsenic-containing iron ore lumps in a beach setting. The exposure scenarios underlying the human health-based risk limits for contaminated land in The Netherlands, based on soil material ingestion and a residential setting, are not appropriate. Two specific exposure scenarios related to the playing with iron ore lumps on the beach ('sandcastle building') are developed on the basis of expert judgement, relating to children in the age of 2 to 12years, i.e., a worst case exposure scenario and a precautionary scenario. Subsequently, exposure is calculated by the quantification of the following factors: hand loading, soil-mouth transfer effectivity, hand-mouth contact frequency, contact surface, body weight and the relative oral bioavailability factor. By lack of consensus on a universal reference dose for arsenic for use in the stage of risk characterization, three different types of assessments have been evaluated: on the basis of the current Provisional Tolerable Daily Intake (PTWI), on the basis of the Benchmark Dose Lower limit (BMDL), and by a comparison of exposure from the iron ore lumps with background exposure. It is concluded, certainly from the perspective of the conservative exposure assessment, that unacceptable human health risks due to exposure to arsenic from the iron ore lumps are unlikely and there is no need for risk management actions.

Forage and rangeland plants from uranium mine soils: long-term hazard to herbivores and livestock?

Metalliferous uranium mine overburden soils integrated into arable land or stabilized by perennial rangeland plants evoke concern about the quality of crops and the exposure of grazing and thereby soil-ingesting (wildlife) herbivores to heavy metals (HM) and radionuclides. In a 2-year trial, thirteen annual and perennial forage and rangeland plants were thus potted on, or taken from, cultivated field soil of a metalliferous hot spot near Ronneburg (Germany). The content of soil and shoot tissues in 20 minerals was determined by ICP-MS to estimate HM (and uranium) toxicities to grazing animals and the plants themselves, and to calculate the long-term persistence of the metal toxicants (soil clean-up times) from the annual uptake rates of the plants. On Ronneburg soil elevated in As, Cd, Cu, Mn, Pb, U, and Zn, the shoot mineral content of all test plants remained preferentially in the range of "normal plant concentrations" but reached up to the fourfold to sixfold in Mn, Ni, and Zn, the 1.45- to 21.5-fold of the forage legislative limit in Cd, and the 10- to 180-fold of common herb concentrations in U. Shoot and the calculated root concentrations in Cd, Cu, Ni, and Zn accounted for phytotoxic effects at least to grasses and cereals. Based on WHO PTWI values for the tolerable weekly human Cd and Pb intake, the expanded Cd and Pb limits for forage, and reported rates of hay, roots, and adhering-soil ingestion, the tolerable daily intake rates of 0.65/11.6 mg in Cd/Pb by a 65 kg herbivore would be surpassed by the 11- to 27/0.7- to 4.7-fold across the year, with drastic consequences for winter-grazing and thereby high rates of roots and soil-ingesting animals. The daily intake of 5.3-31.5 mg of the alpha radiation emitter, U, may be less disastrous to short-lived herbivores. The annual phytoextraction rates of critical HM by the tested excluder crops indicate that hundreds to thousands of years are necessary to halve the HM and (long-lived) radionuclide load of Ronneburg soil, provided the herbage is harvested at all. It is concluded that the content in Cd/As, Cd, and Cu exclude herbage/Ronneburg soil from the commercial use as forage or pasture land soil for incalculable time spans. Caution is required, too, with the consumption of game.

Transfer factors to Whitetail deer: comparison of stomach-content, plant-sample and soil-sample concentrations as the denominator

A recent study measured transfer factors for 49 elements in hunter-killed Whitetail deer (Odocoileus virginianus), using concentrations in the stomach content as the substrate/denominator to compute muscle/vegetation concentration ratios (CR(m-stomach)) and daily fractional transfer factors (Ff). Using the stomach content ensured an accurate representation of what the deer ate, except that it was limited in time to the vegetation selected by the animal just before it was killed. Here, two alternatives are considered, one where the feed is represented by samples of 21 different vegetation types that deer may have eaten in the area (CR(m-plant)), and the other is using soil concentration in the region as the denominator (CR(m-soil)). The latter is the formulation used in the ERICA tool, and other sources, for risk assessment to non-human biota. Across elements, (log) concentrations in all the media were highly correlated. The stomach contents had consistently higher ash and rare earth element concentrations than the sampled (and washed) vegetation and this was attributed to soil or dust ingestion. This lends credence to the use of soil-based CRm-soil values, despite (or more accurately because of) the inclusive yet gross simplicity of the approach. However, it was clear that variation of CR(m-soil) values was larger than for CR(m-stomach) or CR(m-plant), even if soil load on vegetation was included in the latter values. It was also noted that the variation in CR(m-soil) computed from the product of CR(m-plant) and CR(plant-soil) (where CR(plant-soil) is the plant/soil concentration ratio) was somewhat larger than the variation inherent in CR(m-soil) data. Thus it is reasonable to estimate CR(m-soil) from CR(m-plant) and CR(plant-soil) if observed CR(m-soil) values are not available, but this introduces further uncertainty.

Trace elements in feed, manure, and manured soils

Modern animal feeds often include nutritional mineral supplements, especially elements such as Cu, P, Se, and Zn. Other sources of trace elements also occur in livestock systems, such as pharmaceutical use of As and Zn to control gut flora, Bi in dairy for mastitis control, and Cu as hoof dips. Additionally, potential exists for inadvertent inclusion of trace elements in feeds or manures. There is concern about long-term accumulation of trace elements in manured soil that may even exceed guideline "safe" concentrations. This project measured ∼60 elements in 124 manure samples from broiler, layer, turkey, swine grower, swine nursery, sow, dairy, and beef operations. The corresponding feeds were also analyzed. In general, concentrations in manure were two- to fivefold higher than those in feed: the manure/feed concentration ratios were relatively consistent for all the animal-essential elements and were numerically similar for many of the non-nutrient elements. To confirm the potential for accumulation in soil, total trace element concentrations were measured in the profiles of 10 manured and 10 adjacent unmanured soils. Concentrations of several elements were found to be elevated in the manured soils, with Zn (and P) the most common. One soil from a dairy standing yard had concentrations of B that exceeded soil health guideline concentrations. Given that the Cu/P and Zn/P ratios found in manure were greater than typically reported in harvested crop materials, these elements will accumulate in soil even if manure application rates are managed to prevent accumulation of P in soil.

Mass balance soil ingestion estimating methods and their application to inhabitants of rural and wilderness areas: a critical review

Quantitative soil ingestion studies employing a mass balance tracer approach have been used to provide a defensible means to estimate soil ingestion for human health risk assessments. Past studies have focused on soil ingestion in populations living in urban/suburban environments. There is a paucity of reliable quantitative soil ingestion data to support human health risk assessments of other lifestyles that may be predisposed to ingesting soil, such as agricultural workers or indigenous populations following traditional lifestyles. The results of a preliminary analysis of sampling and analytical variability that would result from assessing activities typical of populations in rural or wilderness areas and conducted over wide areas show that approximately 225 subject days would be required to detect a difference of 20mg/d in soil ingestion. Given the typically small populations in these areas, future soil ingestion studies should be focused on specific activities with a high potential for soil ingestion.

[Decision tools for selecting industrial sites where a systematic blood lead screening should be implemented]

BACKGROUND

Children exposure to lead, even at low doses, can induce neurobehavioral and cognitive effects. In France, a consensus conference about lead poisoning in children has recently stated that exposure near an industrial site was a priority for blood lead screening. Selection criteria for industrial sites have therefore to be defined, especially because screening for lead poisoning requires a blood lead sample, that is an invasive procedure.

METHODS

We propose here an operational procedure to select sites where systematic blood lead screenings have to be implemented. It is based on modeling blood lead levels of children aged 1-6 years. This is made by indirect dose estimation from environmental measurements, human exposure parameters and a dose/blood lead level relationship. Decision criteria are based on mean and extreme predicted blood lead level. The procedure is illustrated with a real life smelter case study.

RESULTS

For the studied smelter, estimated blood lead levels are less than 100 microg(Pb)/l(blood) and therefore do not lead to recommend a systematic blood lead screening.

CONCLUSIONS

Indirect dose estimation associated with blood lead level modeling is a useful tool for selecting where blood lead screenings have to be implemented around industrial sites. Possible improvements of the method are listed.

Identifying soil cleanup criteria for dioxins in urban residential soils: how have 20 years of research and risk assessment experience affected the analysis?

This article reviews the scientific evidence and methodologies that have been used to assess the risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and presents a probabilistic analysis for identifying virtually safe concentrations of TCDD toxicity equivalents (TEQ) in residential soils. Updated data distributions that consider state-of-the-science cancer and noncancer toxicity criteria, child soil ingestion and dermal uptake, bioavailability in soil, and residential exposure duration are incorporated. The probabilistic analysis shows that the most sensitive determinants of dose and risk are childhood soil ingestion, exposure duration, and the selected TCDD cancer potency factor. It also shows that the cancer risk at 1 per 100,000 predicted more conservative (lower) soil criteria values than did the noncancer hazard (e.g., developmental and reproductive effects). In this analysis, acceptable or tolerable soil dioxin concentrations (TCDD TEQ) ranged from 0.4 to 5.5 ppb at the 95th percentile for cancer potency factors from 9600 to 156,000 (mg/kg/d)(-1) with site-specific adjustments not included. Various possible soil guidelines based on cancer and noncancer risks are presented and discussed. In the main, the current toxicology, epidemiology, and exposure assessment data indicate that the historical 1 ppb TEQ soil guidance value remains a reasonable screening value for most residential sites. This analysis provides risk managers with a thorough and transparent methodology, as well as a comprehensive information base, for making informed decisions about selecting soil cleanup values for PCDD/Fs in urban residential settings.

Revision and meta-analysis of selected biosphere parameter values for chlorine, iodine, neptunium, radium, radon and uranium

There is a continual supply of new experimental data that are relevant to the assessment of the potential impacts of nuclear fuel waste disposal. In the biosphere, the traditional assessment models are data intensive, and values are needed for several thousand parameters. This is augmented further when measures of central tendency, statistical dispersion, correlations and truncations are required for each parameter to allow probabilistic risk assessment. Recent reviews proposed values for 10-15 key element-specific parameters relevant to (36)Cl, (129)I, (222)Rn, (226)Ra, (237)Np and (238)U, and some highlights from this data update are summarized here. Several parameters for Np are revised downward by more than 10-fold, as is the fish/water concentration ratio for U. Soil solid/liquid partition coefficients, Kd, are revised downward by 10-770-fold for Ra. Specific parameters are discussed in detail, including degassing of I from soil; sorption of Cl in soil; categorization of plant/soil concentration ratios for U, Ra and Np; Rn transfer from soil to indoor air; Rn degassing from surface water; and the Ca dependence of Ra transfers.

Radionuclides in the terrestrial ecosystem near a Canadian uranium mill--Part II: Small mammal food chains and bioavailability

Food chain transfer through the soil-vegetation-small mammal food chain was measured by concentration ratios (CRs) for uranium, 226Ra, 210Pb, and 210Po at three sites near the Key Lake uranium mill in northern Saskatchewan. Plant/soil CRs, animal carcass/GI tract CRs, and animal/soil CRs were depressed at sites impacted by mill and tailings dusts relative to a nearby control site. Thus, radionuclides associated with large particulates in tailings and/or ore dusts may be less bioavailable to terrestrial plants and animals than natural sources of radioactive dust. These results show that reliance on default food chain transfer parameters, obtained from uncontaminated terrestrial ecosystems, may overpredict impacts at uranium mine and mill sites. Given the omnivorous diet of small mammals and birds, animal/soil CRs are recommended as the most cost-effective and robust means of predicting animal concentrations from environmental monitoring data at uranium mill facilities.