Nutrients and non-essential metals in darkibor kale grown at urban and rural farms: A pilot study.

Kale is a nutrient-dense leafy vegetable associated with wide-ranging health benefits. It is tolerant of drought and temperature fluctuations, and could thus serve an increasingly important role in providing a safe and nutritious food supply during the climate crisis, while kale's ease of cultivation and ability to be grown in a wide range of soils make it a good fit for urban agriculture. In this pilot study we explored potential differences between kale grown at urban versus rural farms. We planted kale seedlings (Darkibor variety) at three urban and four rural farms in and around Baltimore City, Maryland, instructed farmers to cultivate them using their usual growing practices, harvested the kale from fields and points of distribution, and analyzed it for concentrations of carotenoids, vitamins C and K1, ten nutritional elements, and eight non-essential metals. Although sample sizes for some analyses were in some cases too small to produce statistically significant results, we identified potentially meaningful differences in concentrations of several components between urban and rural kale samples. Compared to urban samples, mean concentrations of carotenoids and vitamins were 22-38% higher in rural field samples. By contrast, mean concentrations for eight nutritional elements were higher in urban field samples by as much as 413% for iron. Compared to rural field samples, mean concentrations of nine non-essential metals were higher in urban samples, although lead and cadmium concentrations for all samples were below public health guidelines. Some urban-rural differences were more pronounced than those identified in prior research. For six elements, variance within urban and rural farms was greater than variance between urban and rural farms, suggesting urbanicity may not be the primary driver of some observed differences. For some nutrients, mean concentrations were higher than upper ranges reported in prior estimates, suggesting kale may have the potential to be more nutrient-dense than previously estimated. The nutritive and metals composition of this important crop, and the factors that influence it, merit continued investigation given its growing popularity.

Comparative study on changes in Cd accumulation and ionome between rice and spinach: Impact of zinc ion activity.

Excessive Cd accumulation in rice grain has caused chronic Cd diseases in humans. In most crops, 100 times more Zn than Cd strongly inhibits Cd uptake and translocation. However, this response is not found for rice (Oryza sativa L.), which was found to have an unusual Cd uptake pattern compared with other crops, such as spinach (Spinacia oleracea L.). Moreover, studies on shared transporters between Zn and Cd using normal solution experiments with traditional high concentrations of metal ions may result in irrelevant interactions. Therefore, we developed ethyleneglycoltetraacetate-buffered nutrient solutions in this work. Rice and spinach seedlings were grown under calibrated low Cd2+ activity and low to phytotoxic Zn2+ activity levels while buffering other micronutrient cations at sufficient levels. Results showed that as rice grew with pZn2+  = 8.1-5.4, root Cd and shoot Ni decreased significantly and gradually. However, shoot Cd and Mn in rice decreased slightly with the increase of solution Zn2+ from deficiency to sufficiency and then increased at toxic Zn2+ solution (pZn2+  = 5.4). The shoot/root ratios of Cd in rice under toxic pZn2+ (5.6 and 5.4 pZn2+ activity) were significantly increased (p < .05). It could be concluded that rice absorption of Cd is not inhibited by co-contaminating (toxic) Zn. For spinach, with Zn varying from pZn2+  = 8.1-5.7, both shoot and root Cd substantially decreased, as did shoot Ni. This work revealed that, to understand food chain Cd risks, one needs to consider the inhibitory role of Zn in limiting Cd absorption in all crops studied except rice.

Effects of Mn2+ on Cd accumulation and ionome in rice and spinach.

Health risks caused by food containing Cd is a concern worldwide. Interaction between Mn and Cd has been widely studied in normal hydroponic solution with high ion activities (e.g., the study on sharing of transporter Natural Resistance-Associated Macrophage Protein 5 between Mn and Cd in rice [Oryza sativa L.]). However, interaction of Mn and Cd in crops like rice and spinach (Spinacia oleracea L.) at field ion activity level is still unknown. Thus, an ethyleneglycoltetraacetate-buffered solution experiment was conducted to explore the effect of Mn on the uptake and accumulation of Cd and other mineral elements in rice and spinach. In rice, antagonism of Mn and Cd was only observed in roots at deficient and toxic levels of external Mn2+ . Compared with those at Mn2+ sufficiency (pMn2+ 6.7-5.3), average root Cd levels were elevated significantly by 1.85-3.05 times at Mn2+ deficiency (pMn2+ 8.2) but decreased by 1.57-2.59 times at Mn2+ toxicity (pMn2+ 4.8). The antagonism between Mn and K/Mg in rice shoots might be caused by their common role in physiological processes in plants. Antagonism of Mn/Ni in spinach in this work was consistent with their shared transporters in dicots. Results about the antagonism of root Cd/Mn at Mn2+ deficiency suggest that sufficiently available Mn2+ is significant to reduce Cd uptake in rice under field levels of ion activity, but it was not for spinach because the change of tissue Cd was insignificant with the increase of Mn2+ activity from deficiency to toxicity.

The Safe Urban Harvests Study: A Community-Driven Cross-Sectional Assessment of Metals in Soil, Irrigation Water, and Produce from Urban Farms and Gardens in Baltimore, Maryland.

BACKGROUND: Emerging evidence suggests social, health, environmental, and economic benefits of urban agriculture (UA). However, limited work has characterized the risks from metal contaminant exposures faced by urban growers and consumers of urban-grown produce. OBJECTIVES: We aimed to answer community-driven questions about the safety of UA and the consumption of urban-grown produce by measuring concentrations of nine metals in the soil, irrigation water, and urban-grown produce across urban farms and gardens in Baltimore, Maryland. METHODS: We measured concentrations of 6 nonessential [arsenic (As), barium (Ba), cadmium (Cd), chromium (Cr), lead (Pb), nickel (Ni)] and three essential [copper (Cu), manganese (Mn), zinc (Zn)] metals in soil, irrigation water, and 13 types of urban-grown produce collected from 104 UA sites. We compared measured concentrations to existing public health guidelines and analyzed relationships between urban soil and produce concentrations. In the absence of guidelines for metals in produce, we compared metals concentrations in urban-grown produce with those in produce purchased from farmers markets and grocery stores (both conventionally grown and U.S. Department of Agriculture-certified organic). RESULTS: Mean concentrations of all measured metals in irrigation water were below public health guidelines. Mean concentrations of nonessential metals in growing area soils were below public health guidelines for Ba, Cd, Pb, and Ni and at or below background for As and Cr. Though we observed a few statistically significant differences in concentrations between urban and nonurban produce items for some combinations, no consistent or discernable patterns emerged. DISCUSSION: Screening soils for heavy metals is a critical best practice for urban growers. Given limitations in existing public health guidelines for metals in soil, irrigation water, and produce, additional exposure assessment is necessary to quantify potential human health risks associated with exposure to nonessential metals when engaging in UA and consuming urban-grown produce. Conversely, the potential health benefits of consuming essential metals in urban-grown produce also merit further research. https://doi.org/10.1289/EHP9431.

Inter-laboratory validation of an inexpensive streamlined method to measure inorganic arsenic in rice grain.

With the establishment by CODEX of a 200 ng/g limit of inorganic arsenic (iAs) in polished rice grain, more analyses of iAs will be necessary to ensure compliance in regulatory and trade applications, to assess quality control in commercial rice production, and to conduct research involving iAs in rice crops. Although analytical methods using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) have been demonstrated for full speciation of As, this expensive and time-consuming approach is excessive when regulations are based only on iAs. We report a streamlined sample preparation and analysis of iAs in powdered rice based on heated extraction with 0.28 M HNO3 followed by hydride generation (HG) under control of acidity and other simple conditions. Analysis of iAs is then conducted using flow-injection HG and inexpensive ICP-atomic emission spectroscopy (AES) or other detection means. A key innovation compared with previous methods was to increase the acidity of the reagent solution with 4 M HCl (prior to reduction of As5+ to As3+), which minimized interferences from dimethylarsinic acid. An inter-laboratory method validation was conducted among 12 laboratories worldwide in the analysis of six shared blind duplicates and a NIST Standard Reference Material involving different types of rice and iAs levels. Also, four laboratories used the standard HPLC-ICP-MS method to analyze the samples. The results between the methods were not significantly different, and the Horwitz ratio averaged 0.52 for the new method, which meets official method validation criteria. Thus, the simpler, more versatile, and less expensive method may be used by laboratories for several purposes to accurately determine iAs in rice grain. Graphical abstract Comparison of iAs results from new and FDA methods.

Evaluating Leaf and Canopy Reflectance of Stressed Rice Plants to Monitor Arsenic Contamination.

Arsenic contamination is a serious problem in rice cultivated soils of many developing countries. Hence, it is critical to monitor and control arsenic uptake in rice plants to avoid adverse effects on human health. This study evaluated the feasibility of using reflectance spectroscopy to monitor arsenic in rice plants. Four arsenic levels were induced in hydroponically grown rice plants with application of 0, 5, 10 and 20 µmol·L(-1) sodium arsenate. Reflectance spectra of upper fully expanded leaves were acquired over visible and infrared (NIR) wavelengths. Additionally, canopy reflectance for the four arsenic levels was simulated using SAIL (Scattering by Arbitrarily Inclined Leaves) model for various soil moisture conditions and leaf area indices (LAI). Further, sensitivity of various vegetative indices (VIs) to arsenic levels was assessed. Results suggest that plants accumulate high arsenic amounts causing plant stress and changes in reflectance characteristics. All leaf spectra based VIs related strongly with arsenic with coefficient of determination (r²) greater than 0.6 while at canopy scale, background reflectance and LAI confounded with spectral signals of arsenic affecting the VIs' performance. Among studied VIs, combined index, transformed chlorophyll absorption reflectance index (TCARI)/optimized soil adjusted vegetation index (OSAVI) exhibited higher sensitivity to arsenic levels and better resistance to soil backgrounds and LAI followed by red edge based VIs (modified chlorophyll absorption reflectance index (MCARI) and TCARI) suggesting that these VIs could prove to be valuable aids for monitoring arsenic in rice fields.

Growth and Cadmium Phytoextraction by Swiss Chard, Maize, Rice, Noccaea caerulescens, and Alyssum murale in Ph Adjusted Biosolids Amended Soils.

Past applications of biosolids to soils at some locations added higher Cd levels than presently permitted. Cadmium phytoextraction would alleviate current land use constraints. Unamended farm soil, and biosolids amended farm and mine soils were obtained from a Fulton Co., IL biosolids management facility. Soils contained 0.16, 22.8, 45.3 mg Cd kg(-1) and 43.1, 482, 812 mg Zn kg(-1) respectively with initial pH 6.0, 6.1, 6.4. In greenhouse studies, Swiss chard (Beta vulgaris var. cicla), a Cd-accumulator maize (inbred B37 Zea mays) and a southern France Cd-hyperaccumulator genotype of Noccaea caerulescens were tested for Cd accumulation and phytoextraction. Soil pH was adjusted from ∼5.5-7.0. Additionally 100 rice (Oryza sativa) genotypes and the Ni-hyperaccumulator Alyssum murale were screened for potential phytoextraction use. Chard suffered phytotoxicity at low pH and accumulated up to 90 mg Cd kg(-1) on the biosolids amended mine soil. The maize inbred accumulated up to 45 mg Cd kg(-1) with only mild phytotoxicity symptoms during early growth at pH>6.0. N. caerulescens did not exhibit phytotoxicity symptoms at any pH, and accumulated up to 235 mg Cd kg(-1) in 3 months. Reharvested N. caerulescens accumulated up to 900 mg Cd kg(-1) after 10 months. Neither Alyssum nor 90% of rice genotypes survived acceptably. Both N. caerulescens and B37 maize show promise for Cd phytoextraction in IL and require field evaluation; both plants could be utilized for nearly continuous Cd removal. Other maize inbreds may offer higher Cd phytoextraction at lower pH, and mono-cross hybrids higher shoot biomass yields. Further, maize grown only for biomass Cd maximum removal could be double-cropped.

Relating injury to the forest ecosystem near Palmerton, PA, to zinc contamination from smelting.

The forest on Blue Mountain, near Lehigh Gap, has been injured by emissions from two historical zinc (Zn) smelters in Palmerton, PA, located at the northern base of the mountain. The uppermost mineral soil and lower litter from sites along a transect, just south of the ridgetop, contained from 64 to 4400 mg/kg Zn. We measured forest metrics at 15 sampling sites to ascertain how forest structure, species composition and regeneration are related to soil concentrations of Zn, the probable principal cause of the injury. Understanding how ecotoxicological injury is related to soil Zn concentrations helps us quantify the extent of injury to the ecosystem on Blue Mountain as well as to generalize to other sites. The sum of canopy closure and shrub cover, suggested as a broadly inclusive measure of forest structure, was decreased to half at approximately 2060 mg/kg Zn (102 mg/kg Sr(N0(3))(2)-extractable Zn). Tree-seedling density was decreased by 80% (from 10.5/m(2) to 2.1/m(2)) at a much lower concentration: 1080 mg/kg Zn (59 mg/kg Sr(N0(3))(2)-extractable Zn). Changes in species composition and richness were not as useful for quantifying injury to the forest. Phytotoxicity, desiccation from exposure, and a gypsy moth infestation combined to form a barren area on the ridgetop. Liming the strongly acid Hazleton soils at the sites would partially ameliorate the observed phytotoxicity and should be considered in planning restoration.