A problem in conducting realistic toxicity studies is the likely transformation of the free particles into homo or heteroaggregates or even organic complexes in the real environment. There have been few studies that investigated the impact of size across a wide range of systematically varied particle sizes within a single study.On the other hand coating may be an important variable given the extreme sensitivity seen with HMT coated particles in C. elegans.Coating was demonstrated to be a major determinant of toxicity in a more well controlled study that systematically varied coating properties and used coating controls.Of all of the taxonomic groups, toxicity is most well studied in vascular terrestrial plants. Overt phytoxicity of nanoceria seems minimal and, while root to shoot translocation of these particles is often measurable it is generally quite low. In summary, although the literature on nanoceria impacts on terrestrial plants is not extensive, it is clear that overt phytotoxicity is minimal, even at excessive exposure concentrations. The data do suggest accumulation of nanoceria within plant tissues, although the precise form of the element that crosses into the plant and the mechanism driving that process remains unknown. The potential transgenerational effects noted in the literature,as well as the complete lack of information on trophic transfer, are areas of concern. In addition, studies investigating environmentally relevant concentrations, potentially secondary effects from nanoceria exposure, including impacts on symbiotic microorganisms or on edible tissue nutritional quality,vertical farming technology certainly warrant further investigation. As a whole, the aquatic and terrestrial toxicity testing data for animals and microorganisms spans multiple orders of magnitude for acute toxicity values .

This large variation can be exhibited within a single species exposed to similar nanoceria. For example, toxicity values for D. magna range from around 1–100 mg l−1 for fairly similar particles. Based on the overall toxicity database, it appears that C. elegans is the most sensitive animal and Anabaena is the most sensitive microorganism tested to date, although an important caveat is that the same endpoints were not compared across all species and that exposure systems varied. Interestingly no toxicity was observed in the fish species that has been tested even at extremely high exposure concentrations . Unfortunately, only two fish studies have been reported in the literature. There is a complete lack of toxicity testing data for sediment dwelling organisms, and extremely limited data for soil invertebrates. As a whole the data suggest that acute toxicity is possible at low μg L−1 concentrations in the water column. Data are lacking on soils and sediments, but toxicity values are likely to be far lower. One study indicated toxicity at lower concentrations than these values when 8 nm nanoceria were coated with HMT. Since no coating controls were used, it is critical that the influence of this coating and other similar positively charged coatings be studied using a similar endpoint and suitable controls. The use and disposal of any nanoceria containing products with this coating should also be evaluated. It is not clear whether the chronic nature of this exposure or the influence of the coating on uptake and toxicity explain why this toxicity threshold is so low. Although this coating may not persist on the particles in the environment, what is clear is that the effects of chronic dosing and the effects of coating are critical data gaps that should be evaluated. Also completely lacking are more environmentally realistic exposure scenarios, such as ones using natural waters and soils and also multi-species microcosm or mesocosm studies, although such studies are underway. These studies will bring the importance of environmental transformations and indirect ecological impacts into light.

It is possible that community or ecosystem level impacts may be more sensitive than individual level effects. Also more chronic and food chain transfer studies should be encouraged to deal with the possible long term effects from, or accumulations of, the likely persistent nanoceria entities. The current available data do not suggest an immediate risk from acute exposures to nanoceria from use as a fuel additive or mechanical/chemical polishing or planarization. However, the data gaps we have discussed should be addressed before a comprehensive ecological risk assessment can be performed for ceria for chronic exposures or for other exposure pathways. This review lays the foundation for such assessments and clearly identifies the areas where research is most critically needed.n recent years, California has tightened rules for reporting diversions of water for agriculture and other uses. One key challenge has been establishing workable standards for the collection of reliable data on relatively small and remote diversions — such as those for far-flung farms and ranches. Under new legislation, a certification program run by UC Cooperative Extension is helping to solve that problem. The State Water Resources Control Board views accurate diversion reporting as a key element of sound water management. “It’s incredibly important to monitor how much water comes into and goes out of the system,” says Kyle Ochenduszko, chief of water rights enforcement at the water board. Diversion reports are fed into a state database and support the orderly allocation of water resources by, for instance, enabling the board’s Division of Water Rights to inform water users when new requests to appropriate water might affect their own supply. Since 1966, the California Water Code has required diverters of surface water, with certain exceptions, to report their diversions to the water board. But in part because the water board lacked fining authority for many years, compliance was poor. In 2009, Senate Bill 8 gave the water board the authority to fine non-compliant diverters an initial $1,000, plus $500 for each additional day of failing to report. Even so, SB 8 did not stipulate precisely how diversions were to be monitored. Rather, it required diverters to measure their diversions using the “best available technologies and best professional practices,” unless they could demonstrate that such technologies and practices were not locally cost-effective.

That is, the requirement left wide latitude for interpretation. So things remained until 2015 — when Senate Bill 88 became law. This piece of legislation, passed amid a historically severe drought, directed the water board to draw up emergency regulations regarding water diversions. The regulations, once completed, required diverters of at least 100 acre-feet of water per year to hire an engineer or appropriately licensed contractor to install all monitoring devices. Now the requirements were clear. But the provision mandating installation by an engineer or contractor prompted an outcry from many smaller diverters, particularly those in remote areas of the state. For most diverters near sizable towns — Redding, say — complying with the regulations was manageable, with expenses limited to the cost of a monitoring device and the services of an installer. But diverters in remote parts of Modoc County, for example, were looking at bigger bills,vertical tower planter says Kirk Wilbur of the California Cattlemen’s Association. For such diverters, compliance might require importing an engineer or contractor from far away, which would entail significant travel expenses. If a site lacked electricity, as many do, the costs would pile higher . So how to reconcile the interests of the state’s diverters with those of the state? How best to balance the public and the private good? The answer, it turned out, was to empower diverters to install their own monitoring devices — with UCCE playing the empowering role. The idea originated with the Shasta County Cattlemen’s Association. It gained in soil contain significant amounts of Si. Almost 150 years ago, Julius Sachs raised questions about the role of Si as to “whether silicic acid is an indispensable substance for those plants that contain silica, whether it takes part in the nutritional processes, and what is the relationship that exists between the uptake of silicic acid and the life of the plant?” . These questions are still valid and require an intensive investigation about the role of Si in plant physiology and biochemistry. In nature, Si is not an inert element and its bio-active role in plants under various biotic and abiotic stresses is more evident . But there is contradiction about the direct role of Si in plants as a nutrient. There is some evidence that Si can have an impact on plant growth by changing photosynthetic activity and by changing cell wall extensibility in young growing regions of root and shoot . Fauteux et al. showed, using a micro-array expression, that only two genes were affected when Si was supplied under no-stress conditions. In contrast, plants inoculated with a fungus and treated with Si altered the expression of nearly 4,000 genes. So a study was planned to investigate whether there is a direct effect of Si on growth of maize under normal growing conditions. Food borne illness is one of the most serious health problems worldwide, affecting public health and development . Salmonella spp. and pathogenic Escherichia coli strains are two of the main bacterial pathogens causing food borne diseases . Worldwide, it is estimated that Salmonella is responsible for 80.3 million cases of food borne illness . Raw fruits and vegetables are increasingly recognized as an important source of food borne disease outbreaks in many parts of the world . Leafy vegetables were identified as the fresh produce commodity group of most significant concern from a microbiological safety perspective . Consequently, recent studies have focused on understanding the interactions between human pathogens and plants . Leaf attachment and internalization enable bacteria to get a foothold on the leaf surface and potentially reach the leaf interior .

The ability of both plant and human pathogens to reach the leaf interior is considered an important virulent trait, as internalized bacteria gain access to the nutrient-rich milieu within the leaf tissue and are protected against external environmental stresses, such as desiccation, irradiation, starvation, competition, and predation. Salmonella enterica and E. coli can internalize the plants through natural openings, such as hydathodes, stomata, lenticels, lateral root emergence sites, or sites of biological or physical injury . A common method to assess leaf internalization is by taking advantage of the resistance of the internalized bacteria to surface disinfection . Following inoculation of the pathogen of choice, surface-attached bacteria are killed by exposing the plants or plant’s organ to disinfecting agents. The plant tissue is then macerated to release the internalized bacteria and the disinfectant-protected bacteria are then enumerated by viable count, e.g., plating the homogenate on appropriate agar media. The viable count technique is straightforward and easy to perform and, consequently, it was widely adopted in studies assessing leaf internalization by enteric pathogens . However, a major caveat of this method is that the results depend on the conditions used for surface sterilization, e.g., type of disinfectant and treatment duration, which require validation for each specific combination of bacterial strain and plant cultivar. A literature review showed that only a few studies had validated the complete inactivation of surface-attached enteric bacteria, while in most cases, surface sterilization conditions were based on previously reported protocols, or the validation data were not presented . Another approach to assess leaf internalization by food borne pathogens is confocal microscopy. This method utilizes fluorescence-tagged bacteria and enables direct and precise localization of the bacteria within the leaf tissue. Nevertheless, it is time-consuming and requires expensive equipment and expertise. Commonly, confocal microscopy provides supportive data to confirm the internal localization of the tested bacteria and validate complete inactivation of surface-attached bacteria . In some cases, confocal microscopy may also provide quantitative data regarding leaf internalization . In a previous study, employing confocal microscopy, we compared the internalization of S. enterica serovar Typhimurium, through stomata, in various leaves and found that it efficiently internalizes lettuce leaves but virtually failed to internalize tomato leaves, based on visualization of at least 360 microscopic leaf fields obtained from three plants . It should be noted that numerous factors, such as bacterial strain, plant cultivar, growing conditions, age, epiphytic and endophytic flora, mode of inoculation, and other experimental factors, might affect the level and quantification of leaf internalization ; yet validated data regarding the efficacy of a given protocol to assess bacterial internalization in different plant models are scarce. In the present study, we have employed an in vitro model system to systematically examine Salmonella stomatal internalization in tomato, lettuce, and Arabidopsis thaliana leaves using a specific Salmonella strain with three surface sterilization protocols, side by side with confocal microscopy validation.