The reduced bio-degradation in the SB microcosms may have resulted from the ~40% higher carbon content in the SB microcosms, which would be expected to increase the soil-water distribution coefficient by a comparable amount. Reduced TCS concentration in soil pore water would be expected to slow bio-transformation, potentially in a nonlinear fashion. Another possible contributor to the slower degradation of TCS in SB is the greater availability of alternative, likely more easily degradable, carbon sources in SB than soil microcosms, reducing the use of TCS as a substrate. Selective bio-degradation of one carbon source, and inhibition of the degradation of other chemicals also present, has been observed for mixtures of chemicals in aquifers . To assess which of these mechanisms was controlling, measured Freundlich isotherm parameters for TCS adsorption on bio-solid amended Yolo soil were used to calculate equilibrium pore water concentrations in the soil and SB microcosms over the course of the experiment. Using estimated pore water concentrations of moistened soil and SB samples,pe grow bag instead of total soil concentrations to perform half-life calculations, resulted in modest increases in the rate constants and decreases in half-lives of soil samples and did not narrow the significant gap between half lives in soil and SB .
This suggests that the primary reason for the slower degradation of TCS in bio-solid amended soils is the increase in more labile forms of carbon because organic material is highly porous and has a lower particle density. Previous research shows that TCS biodegrades within weeks to months in aerobic soils , although Chenxi et al., found no TCS degradation in bio-solids stored under aerobic or anaerobic conditions, Kinney et al., observed a 40% decrease in TCS concentrations over a 4-month period following an agricultural bio-solids application. Because the slopes of the lines in Fig. 1 are not significantly different as a function of spiking level , the slopes were averaged for each treatment type, yielding apparent first order rate constants of 0.093±4% d−1 for soil samples and 0.024±41% d−1 for SB samples where the percent error represents the relative percent difference between the 10 mg/kg and 50 mg/kg degradation curves. These apparent rate constants translate to half-life estimates of 7.5 d in soils and 29 d in bio-solid amended soil. The estimated half-life of TCS in soil is within the range of previously reported half-lives of from 2.5 to 58 d in soil . The half-life determined here in bio-solid amended soils is lower than the one available literature value of 107.4 d . The microbial biomass decreased in the TCS spiked samples after 7 or 30 days of incubation in comparison with the unspiked controls, for both soil and SB, and the decline was statistically significant at 50 mg/kg .
Although exposure to TCS caused declines in biomass in both soil and SB microcosms, the total microbial biomass was two times higher in SB than soil probably due to the increased availability of nutrients and/or possibly due to addition of bio-solid associated microorganisms in the latter . The total number of PLFAs ranged from 42–47 in soil and 48–59 in SB . No significant change in numbers of PLFAs was evident with increasing dosage of TCS for any incubation time suggesting that TCS addition did not adversely affect microbial diversity. Microbes respond to various stresses by modifying cell membranes, for example by transforming the cis double bond of 16:1ω7c to cy17:0, which is more stable and not easily metabolized by the bacteria, reducing the impact of environmental stressors . Consequently, the ratio of cy17 to its precursor has been employed as an indicator of microbial stress that has been associated with slow growth of microorganisms . Increases in this stress biomarker were observed in both soil and SB samples as TCS concentrations increased , suggesting that TCS has a negative effect on the growth of soil microorganisms. The overall level of cy17 to its precursor is lower in SB than soil samples, suggesting that nutrients contributed by the bio-solids reduce stress on the microbial community. Our study agreed with a previous study showed that carbon added to soil led to a reduction in the cy17 fatty acid TCS additions, however, increased the stress marker compared with that detected in the corresponding samples with no added TCS.
A broader implication of this result is that presence of bio-solids may mitigate the toxic effects of chemicals in soil, or chemicals added in combination with bio-solids, on soil microbial communities. Groupings of microbial communities, based on CCA analysis of their composition as estimated by PLFA, were distinguished primarily by whether they were in soil or SB treatments and secondarily by time since spiking . To isolate the effects of bio-solids and TCS amendments on microbial community composition, the data was analyzed using pCCA considering TCS and bio-solid amendment as environmental variables, and incubation time as a covariable . This confirmed the results of the CCA indicating that the strongest determinant of microbial community composition was addition of bio-solids to soil. TCS concentration, on the second axis, described only 3.6% of the variation, showing TCS effects were overshadowed by the effects of bio-solid amendment. Bio-solid amendments caused an approximately two-fold increase in PLFA biomarkers for Gram-positive bacteria, actinomycetes and eukaryotes in SB compared to soil samples . Even larger increases were observed in biomarkers for fungi and Gram-negative bacteria, which were up to three times higher in SB than soil. Again, these changes were likely due to increased nutrient availability in the bio-solid amended samples and/or the biomass added along with the bio-solids, growing bags consistent with previous studies that found that the fatty acid 18:2 ω6, 9c and monounsaturates were increased by addition of these materials . The effect of TCS on microbial community composition was greater in soil than SB. Spiking with 10 or 50 mg/kg TCS decreased the abundance of Gram positive and Gram negative bacteria as well as fungi, with reductions ranging from 14 to 27% by day 30. Additionally, actinomycetes, which are Gram positive bacteria, were reduced in the 50 mg/kg TCS samples after 30 days of incubation . Eukaryotes were negatively affected after 7 and 30 days of incubation at both concentrations of TCS in soil but not SB samples. Biomass results for all microbial groups were consistent in suggesting that the presence of bio-solids mitigated the potential toxicity of TCS. It is important to note that the spiking levels used here are similar to levels found in the upper half of U.S. bio-solids, but would be unlikely to be achieved in bio-solid amended soils even after continued long term application. Therefore, the effects observed at the 10 or 50 mg/kg spiking levels should be viewed as a conservative upper bound on potential effects expected in the field. In addition, since all of the results in this study are based on an observation period of 30 d, the extent to which the observed effects persist is not known. Future studies should, in particular, investigate longer term changes in community structure in response to addition of bio-solids both with and without specific contaminants.
Over the past 30 years, nanoparticle engineering has led to the development of novel delivery systems for active ingredients with medical, veterinary, and agricultural applications. The increasing cost of research and development combined with the growing number of competitive manufacturing entities, short patent cycles, and the tightening regulatory guidelines for active ingredients, have made it difficult to bring new formulations from the bench to the market.Furthermore, the efficacy of many drugs is limited by their low solubility and/or stability, as well as off-target effects following systemic delivery. For example, cancer therapy is often unsuccessful due to the toxicity of cancer drugs towards healthy cells and/or the development of resistant cells over expressing efflux transporters and multi-drug-resistance proteins.The resulting low bio-availability of the active ingredient in the tumor requires the administration of larger doses to ensure the drug concentration stays within the therapeutic window, which in turn increases off target toxicity. Nanocarriers can address this challenge by delivering active ingredients via the enhanced permeability and retention effect, a well-established phenomenon based on the combination of leaky vasculature and poor lymphatic drainage at the tumor site.The EPR effect only increases the tumor homing of nanoparticles by two-fold compared to normal tissue,so nanoparticles can also be functionalized with targeting ligands, aptamers, antibodies, or antibody fragments to promote their binding to receptors overexpressed on tumor cells or in the surrounding extracellular matrix.The entrapment of active ingredients in nanocarriers also reduces the clearance rate via renal elimination and phagocytosis, which increases the active ingredient circulation time and therefore its therapeutic longevity. The medical and veterinary applications of nanocarriers are analogous, but only experimental veterinary applications have been reported.Most research in veterinary drug delivery has focused on diseases in animals that can be translated to humans. However, the importance of animal welfare per se is increasingly important to consumers, and nanocarriers that improve the efficacy and safety of active ingredients are demanded in the context of companion animals such as cats, dogs and horses, as well as farm animals such cattle, sheep, swine and poultry.Pet owners consider companion animals as an extension of the family and are willing to pay their bills, including the high cost of cancer treatment, with the cost of veterinary care in the USA therefore rising from $7 billion in 2001 to $19 billion in 2019.This increase most likely reflects a combination of inflation, high drug costs, better treatment options , and an increased willingness to care for pets. In contrast, the food industry works with low profit margins and would only treat animals suffering from temporary and low-risk diseases, such as infections.Veterinary nanocarriers must therefore combine low costs with the release of active ingredients for sustained periods to minimize the frequency of animal handling and improve therapeutic efficacy. For example, animals are often subject to bacterial infections, and a nanomedicine approach could achieve the targeted delivery of drugs to pathogens, killing them on demand. This avoids the unnecessary use of antibiotics, which can encourage the emergence of resistant strains. The controlled delivery of agrochemicals and nutrients to plants is conceptually similar to drug delivery in humans and animals. However, agricultural delivery takes place in an open field, with variable weather and geographic features and no specific transport pathway to the target, in contrast to the closed and regulated nature of the bloodstream. Nanocarriers can be administered via the foliage, where they are taken up passively through stomata and any wounds, or can be transported through the soil and taken up via the roots.Among the agrochemicals that can be delivered using nanoparticles, pesticides are particularly suitable candidates because they are effective at very low doses but are difficult to apply in such small amounts due to their non-uniform distribution in the field.To compensate, the active ingredient can be diluted within a mixture of liquid or solid diluents. However, the active ingredient is often unstable, sparingly soluble, and binds with high affinity to soil particles, thus reducing its efficacy against target pests and increasing the amount required to achieve an effective dose.In an analogous manner to the off-target effects caused by systemic drugs, the persistence of large quantities of pesticides in the environment is toxic to other species, and contaminates the soil and groundwater leading to health problems in domestic animals and humans, including cancer and infertility.In one strategy, the active ingredient is enveloped in organic or inorganic coatings for protection against photolysis or bio-degradation, allowing the controlled release of the ingredient.But even microencapsulation is limited by the poor chemical and thermal stability of the capsules, and degradation promotes the acidification of soil, which can impair its fertility. As discussed in more detail below, these drawbacks can be addressed by a new generation of nanocarriers based on polymers, lipids and other materials. The definition of a nanomaterial is not yet harmonized, but the International Organization for Standardization defines nanoparticles as objects with dimensions of 1–100 nm, because the physicochemical properties of the material at this scale differ from the bulk material. Unfortunately, this ISO definition excludes most nanomaterials that are relevant in the medical, veterinary, and agricultural sectors.