Agricultural Food Chain Research Articles

The chemical form of trivalent chromium in xylem sap of maize (Zea mays L.)

The toxicity, mobility and bioavailability of Cr, a versatile industrial metal and a contaminant, depends on its chemical form, viz: Cr(lll) and Cr(VI). It may enter humans through plants grown on contaminated soil or irrigated by contaminated water. The phytoavailability and transfer through agricultural food chains requires an understanding of mechanisms of Cr uptake and translocation by plants. Xylem sap transports both nutrient and non-nutrient ions after absorption by roots to aerial parts of the plant. lt transports cations by complexation with organic ligands. Trivalent chromium, though prone to hydrolysis, also complexes O donor ligands. The chemical form in which Cr(lll) is transported by xylem sap was investigated. ln vitro studies were performed by mixing the xylem sap of maize plants at three stages of plant growth with radiotagged Cr(III). The speciation change was investigated after 10 days and 30 days by anion and cation exchange elution chromatography. The elution curves were compared with those of pure Cr(III) and Cr(III) complexes of different synthetic acids. Complexation of Cr(III) with ligands of xylem sap especially with carboxylates was evident. Cationic Cr(III) was vitally being transported as anionic organic complex species. The major species seemed to be that of Cr(III)-citrate. Citric acid was the major complexing acid of xylem sap as determined by HPLC. These mobile and soluble complexes may get immobilized and stored in leaves and other edible plant parts. This may also be a mechanism used by plants for detoxification of toxic Cr(VI) which may become reduced and then complexed.

A food chain model to predict the levels of lipophilic organic contaminants in humans

A fugacity-based, nonsteady state, mechanistic model called ACC-HUMAN was developed to describe bioaccumulation of lipophilic organic pollutants from air, water, and soil to humans. The physical environment was linked via a marine and an agricultural food chain model to a human bioaccumulation model. Contaminant uptake via the primary dietary sources of persistent lipophilic contaminants in industrialized countries was addressed, namely fish, dairy products, and beef. In addition, uptake from air and water was considered, allowing the model also to treat less lipophilic compounds. To evaluate the model, the food chain characteristics were parameterized for southern Sweden and historical scenarios of polychlorinated biphenyl (PCB) concentrations in air, water, and soil in this region were constructed from published data. The resulting model predictions of PCB concentrations in fish, milk, beef, and human tissue agreed well with measured concentrations from Swedish monitoring programs. This suggests that ACC-HUMAN is a useful tool for predicting human exposure to bioaccumulative organic compounds. It can be linked easily to existing multimedia fate and transport models.

Bioaccumulation potential of persistent organic chemicals in humans.

A model was used to explore the influence of physicalchemical properties on the potential of organic chemicals to bioaccumulate in humans. ACC-HUMAN, a model of organic chemical bioaccumulation through the agricultural and aquatic food chains to humans, was linked to a level I unit world model of chemical fate in the physical environment and parametrized for conditions in southern Sweden. Hypothetical, fully persistent chemicals with varying physical-chemical properties were distributed in the environment, and their bioaccumulation to humans was calculated. The results were evaluated using the environmental bioaccumulation potential (EBAP), defined as the quotient of the chemical quantity in a human divided by the quantity of chemical in the whole environment. Since the latter is closely related to emissions, EBAP is potentially a more useful tool for comparative risk assessment of chemicals than currently used medium-specific measures such as the fish-water bioaccumulation factor. A high environmental bioaccumulation potential, defined as > 10% of the maximum EBAP, was found for chemicals with 2 < log KOW < 11 and 6 < log KOA < 12. While these chemical partitioning properties clearly influenced bioaccumulation at each trophic level, these effects tended to equalize over the food web. The fact that the transfer from the environment as a whole to humans was quite uniform over a large chemical partitioning space suggests that these partitioning properties are relatively unimportant determinants of human exposure compared to other factors such as the substance's persistence in the environment and in the food web.

Trace elements in soils and plants: An overview

The movement of both essential and non‐essential trace elements through agricultural ecosystems and food chains is a complex phenomenon. Such elements as As, B, Cd, Cr, Cu, Hg, Ni, Pb, Se, U, V, and Zn, are generally present in soils in low concentrations but concentrations may be elevated because of natural processes and human activities, such as fossil fuel combustion, mining, smelting, sludge amendment to soil, fertilizer application, and agricultural practices. Although a significant effort has been expended over the past 40 years to evaluate and quantify the transfer of trace elements from soils to plants, more attention needs to be given to mechanisms within the soil and plant systems, which influence their solubility, chemical speciation, mobility, and uptake by and transport in plants. The prediction of movement of trace elements in the agricultural ecosystem must be partially based on understanding the soil and plant processes governing chemical form and the uptake and behavior of trace elements within plants.

Modelling the fate and behaviour of lipophilic organic contaminants in lactating dairy cows

Meat and dairy products are a key source of human exposure to persistent lipophilic organic contaminants (e.g. PCBs, PCDD/Fs). The primary source of these contaminants to beef and dairy cows is the ingestion of contaminated herbage and supplementary feeds. In turn, herbage is primarily supplied with such contaminants via atmospheric deposition. An in-depth understanding of the transfer of semi-volatile contaminants (SOCs) from air–grass–cow–human is therefore required to quantify and manage this exposure pathway. This paper is concerned with modelling/predicting milk and tissue contaminant burdens, given information on measured herbage concentrations. As a result of numerous studies on the transfer of organic contaminants within agricultural foodchains (e.g. Fries, 1977; Fries, 1995; McLachlan, 1993; Olling et al., 1991) generic models are available in the literature. This paper critically reviews the commonly used modelling approaches and examines their predictive capabilities. The influence of natural variability, due to environmental factors and farming practice, on the contaminant composition of milk is investigated. The paper has implications for regulatory authorities, and others, who may have to take a `grab' sample of milk, whether from a bulk collection tank or an individual animal, and then make an assessment on the contaminant status of the herd, and the implications of the consumption of the milk by the general population.

Soil/Air Partitioning of Semivolatile Organic Compounds. 1. Method Development and Influence of Physical−Chemical Properties

Soil is the primary sink of semivolatile organic compounds (SOCs) in the terrestrial environment, while the atmosphere is the primary vector of these substances to humans via the agricultural food chain. Hence, the exchange of SOCs between soil and air is of paramount importance to their environmental fate and potential risk to humans. In this paper, a method is developed to determine soil/air partition coefficients (KSA) of SOCs. On the basis of the solid-phase fugacity meter developed for plants, the method was initially tested using a soil contaminated in the laboratory with chlorinated benzenes, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. A systematic validation exercise demonstrated that the method is not subject to a wide range of potential artifacts. It was then shown that KSA in moist soil (relative humidity = 100%) is independent of the water content of the soil. The method was then extended to the measurement of KSA in the original soil, which contained background levels of ...

A novel and simple model of the uptake of organic chemicals by vegetation from air and soil

A novel and simple three-compartment fugacity model has been developed to predict the kinetics and equilibria of the uptake of organic chemicals in herbaceous agricultural plants at various times, including the time of harvest, using only readily available input data. The chemical concentration in each of the three plant compartments (leaf, stem which includes fruits and seeds, and root) is expressed as a function of both time and chemical concentrations in soil and air. The model was developed using the fugacity concept; however, the final expressions are presented in terms of concentrations in soil and air, equilibrium partition coefficients and a set of transport and transformation half-lives. An illustrative application of the model is presented which describes the uptake of bromacil by a soybean plant under hydroponic conditions. The model, which is believed to give acceptably accurate prediction of the distribution of chemicals among plant tissues, air and soil, may be used for the assessment of exposure to, and risk from contaminants consumed either directly from vegetation or indirectly in natural and agricultural food chains.

A simple model to predict accumulation of PCDD/Fs in an agricultural food chain

The accumulation of PCDD/Fs in the air-soil/feed-cattle-beef/milk agricultural food chain is described. A simple model describing the accumulation through the food chain is presented. The model is employed to predict the concentrations of PCDD/Fs in milk and beef in Germany and found to be in very good agreement with measured concentrations from monitoring studies.

Exploring the Balance between Sources, Deposition, and the Environmental Burden of PCDD/Fs in the U.K. Terrestrial Environment: An Aid To Identifying Uncertainties and Research Needs

The United Kingdom is used as a study area in which to examine (i) the relationship between primary and potential secondary emissions of PCDD/Fs; (ii) the balance between atmospheric emissions and deposition; and (iii) the contemporary environmental burden of PCDD/Fs and possible historical input profiles. This critical review exercise is seen as an important aid to identifying gaps in knowledge and research needs and directing a scientifically sound strategy for PCDD/F risk reduction. The paper focuses on two key compartments, air and soil, as these play an important role in the movement and storage of PCDD/Fs. The terrestrial agricultural food chain supplies the majority of human exposure to PCDD/Fs via the pathway air−deposition−crop/pasture/soil−grazing animals−meat/dairy products−human diet. Primary emissions of PCDD/Fs to the atmosphere are expected to decline in the future following the implementation of new legislative controls. This should be reflected by a further decline in ambient air concentrations, as our calculations indicate that primary emissions are currently the main PCDD/F sources to air. The soil burden will take much longer to decline, due to the extreme persistence of these compounds in this environmental matrix. The paper highlights uncertainties and future research needs concerning the environmental sources, fate, and behavior of this group of compounds.

Human Contributions to Terrestrial Nitrogen Flux

This article assesses the sources and fates of anthropogenic fixed nitrogen. Anthropogenic nitrogen from most sources comes together in the common pathways of the agricultural food chain. The topics covered in this article include the following: inputs of newly fixed nitrogen; nitrogen flow in agriculture; calculating production of plant nitrogen; calculating consumption of nitrogen; harvests and grazing and the effect on nitrogen; nitrogen flow through livestock; net trade; nitrogen flows in regions of the United States; riverine discharges. 51 refs., 4 figs., 4 tabs.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in sewage sludge: sources and fate following sludge application to land

Municipal sewage sludge is ubiquitously contaminated with polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDF). Whereas in Germany there are some industrial sources, associated in particular with the use of pentachlorophenol (PCP) in the textile industry, surface runoff and household wastewater play a more important role in most treatment plants. Most of the higher chlorinated PCDDF congeners in sludge originate in textiles which become contaminated during production through the use of PCP. The PCDDF, which are contaminants in technical PCP, are washed out of textiles in the washing machine and enter household wastewater. The lower chlorinated PCDDF, on the other hand, reach sludge largely as the result of transport of atmospheric deposition to the treatment plant in surface runoff. Following application of sewage sludge to land, the PCDDF are very persistent, with half lives in excess of 10 years. They accumulate in soils and can under some conditions enter the agricultural food chain. The potential risk of land application of sewage sludge increasing human exposure to PCDDF depends on the level of sludge contamination, the intensity of sludge use and the agricultural practices.

Vertical cooperation in agricultural production-marketing chains, with special reference to product differentiation in pork

Optimization of individual stages within a production-marketing chain (PMCh) may cause a suboptimal result of the PMCh as a whole. Market imperfections and conflicting interest may be the causal factors. Although vertical integration is often mentioned as the conventional solution, certain disadvantages and the large scale differences in agricultural PMChs make vertical cooperation a more appropriate alternative. Moreover, specific characteristics of agricultural food chains and changing market circumstances, including increased interest in the quality of products and production processes, justify renewed attention to vertical cooperation and product differentiation in agriculture. Current developments in the Dutch pork PMCh and implications on future research are described. © 1996 John Wiley & Sons, Inc.

Bioaccumulation of Hydrophobic Chemicals in Agricultural Food Chains

The bioaccumulation of polychlorinated biphenyls, dibenzo-p-dioxins, dibenzofurans, and hexachlorobenzene in an air−plant/soil−cow−human food chain was examined using field data collected in southe...

Determination of the Principal Pathways of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans to Lolium multiflorum (Welsh Ray Grass)

This study presents experimental evidence that dry gaseous deposition is the dominant pathway of relatively involatile organic contaminants like polychlorinated dibenzo-p-dioxins and dibenzofurans to Welsh ray grass, an important species in agricultural food chains. The uptake pathways of these compounds to Welsh ray grass were studied under near natural conditions using a system of greenhouses and outdoor plots. Dry gaseous deposition was found to be the principal pathway of Cl 4 -Cl 6 DD/F to the grass leaves. The contribution of dry deposition of small particles (<2.9μm)to the grass levels was negligible for all compounds studied. There was some evidence that the deposition of large particles was an important pathway for the uptake of Cl 7 DD and Cl 8 DD, particularly during the autumn period when the particle-bound concentrations of these compounds were higher. Soil-related pathways did not measurably influence the substance levels in the grass.

Disposition of toxic metals in the agricultural food chain. 2. Steady-state bovine tissue biotransfer factors

Disposition of toxic metals in the agricultural food chain. 2. Steady-state bovine tissue biotransfer factors

Monitoring and assessment of mercury pollution in the vicinity of a chloralkali plant. II Plant-availability, tissue-concentration and genotoxicity of mercury from agricultural soil contaminated with solid waste assessed in barley ( Hordeum vulgare L.)

Barley ( Hordeum vulgare L.) was used to assess plant-availability, tissue-concentration and genotoxicity of mercury from the solid waste deposits of a chloralkali plant. Seeds of H. vulgare, presoaked in distilled water, were allowed to germinate and grow on agricultural soil mixed with solid waste containing 2550 ± 339 mg Hg kg −1 at different proportions (0·75, 1·5, 2·5 and 5%). Plants raised from germinating seeds on uncontaminated agricultural soil served as controls. On day 7, germination counts and seedling heights were recorded. The concentration of mercury in soil, and plant tissue (dry weight) were determined at different stages of plant growth from day 7 till maturity and harvest. The availability of mercury from the soil was assessed by extracting mercury at a range of pH values (2–6) and by chemical methods. The embryonic shoots excised at 36 h of germination were subjected to cytological analysis to determine mitotic index and frequency of mitoses with chromosomal aberrations. The pollen mother cells from anthers of young M 1-spikes were analysed to score meiotic aberrations. Subsequently, the pollen fertility and seed set were determined. Furthermore, M 2-seedlings were analysed for chlorophyll-deficient mutations. The cytogenetic analysis revealed the effects of mercury on the mitotic and meiotic chromosomes which were significantly correlated with soil-mercury. The bioconcentration of mercury in aerial tissues decreased with the age of the plant. Roots, in particular, were found to concentrate most of the mercury taken up by the plant. At the time of harvest, the bioconcentration of mercury in straw was at a minimum. The accumulation of mercury in grain, which was significant, did not increase with the increase in concentration of mercury in soil but maintained a plateau, indicating a restriction of transport of mercury through the phloem. The unique advantage with the use of Hordeum assay is that, besides assessing the germline toxicity, the assay takes into account the possible contamination of the agricultural food-chain.

Disposition of toxic metals in the agricultural food chain. 1. Steady-state bovine milk biotransfer factors

Pharmacokinetic analyses were conducted on published experimental data to estimate steady-state bovine milk biotransfer factors for six metals-arsenic, cadmium, chromium, lead, mercury, and nickel. Both long-term feeding studies and bolus oral dose date were evaluated. This analysis indicated that, of the metals studied, lead and arsenic transfer to milk to the greatest extent, followed by chromium, mercury, and cadmium. The lead biotransfer factor is approximately 50 times that calculated for cadmium. Insufficient information was available to calculate an accurate biotransfer factor for nickel. Metals, as components of sludge (particularly lead, arsenic, and cadmium), were not found to produce significant elevations in analyte concentrations in milk. These findings suggest that metals contained in sludge may not be as bioavailable to dairy cows as metal salts.

PCDD/F in an agricultural food chain Part 1: PCDD/F mass balance of a lactating cow

A mass balance was conducted of the PCDD/F fluxes into and out of a lactating cow in an unmodified environment. Feed was found to be responsible for virtually all of the cow's PCDD/F exposure. Approximately 20% of the 2,3,7,8-Cl 4DD toxic equivalents taken up by the cow was excreted in the milk. The measured transfer rates for a cow in a natural state generally agreed well with the results from feeding experiments in the literature. The digestive tract resorption of PCDD/F decreased with increasing degree of chlorination. Both the feces and the milk were important routes for the excretion of persistent PCDD/F isomers.

Biological Monitoring of an Agricultural Food Chain: Soil Cadmium and Lead in Ruminant Tissues

AbstractLow‐level contamination of a sandy soil with toxicants Cd and Pb at 0.01 to 9.0 and 3.0 to 54.0 mg kg−1 soil induced a significant toxicant accumulation in sudan‐sorghum hay [Sorghum sudanense (Piper) Stapf‐S. bicolor (L.) Moench] (0.5–5.0 and 0.2–1.5 mg kg−1 dry biomass), respectively. Ingestion of 22 to 222 mg Cd kg−1 body wt. by pregnant dairy goats (Capra hircus) from the consumption of hay over 98 d resulted in a significant, but relatively diminutive accumulation of Cd in the doe livers (0.01–0.02 mg kg−1) and brain cortex (0.002–0.007 mg kg−1) fresh wt., but not in doe kidneys and blood averaging 0.028 and 0.002 mg Cd kg−1 fresh tissues, respectively. Fetal blood and liver accumulated 2.0 and 4.0 mg Cd kg−1 fresh tissue, respectively, and fetal kidney exhibited a weak response (0.03–0.47 mg Cd kg−1 fresh tissue) to Cd ingested by the pregnant does. Consumption of 240 to 1230 µg Pb kg−1 body wt. induced 1.0 to 43.0 mg Pb kg−1 fresh tissue in the doe brain cerebellum, but not in the doe liver and blood averaging 0.09 and 0.017 mg Pb kg−1 fresh tissue, respectively. Fetal liver and blood averaged 0.043 and 0.014 mg Pb kg−1 tissue. Only minuscule amounts of soil Cd and Pb were retained in the select animal tissues via the ingestion of this hay. Only one‐ten‐millionth of labile soil Cd and Pb, respectively, accumulated in the select tissues of the pregnant does via the hay pathway. All these amounts were comparable to the norm. If these select animal tissues were used as food, no deleterious effect to human health should be induced.

Dioxin in the agricultural food chain.

Polychlorinated dibenzo-p-dioxin's (PCDD) behavior in the agricultural food chain was modeled in this study. The source of PCDD was a municipal solid waste (MSW) incinerator. Of the farm livestock investigated only the beef cow and the milk cow were shown to contribute significant amounts of PCDD to humans. Milk was the single highest dietary source of PCDD. Comparison of the calculated human dose of PCDD from the agricultural food chain with an estimate human PCDD dose from inhalation of contaminated air revealed that the agricultural food chain could be responsible for a vast majority of the dose to an individual impacted by these facilities. Thus, these data suggest that operating MSW facilities in agricultural areas may result in enhanced PCDD exposure to individuals via the agricultural food chain. The data also suggest that milk and beef may be good sentinels to evaluate environmental impacts of these facilities.