Actual Bioavailability Research Articles

A Stable and Sensitive Engineering Bacterial Sensor via Physical Biocontainment and Two-Stage Signal Amplification.

Although engineering bacterial sensors have outstanding advantages in reflecting the actual bioavailability and continuous monitoring of pollutants, the potential escape risk of engineering microorganisms and lower detection sensitivity have always been one of the biggest challenges limiting their wider application. In this study, a core-shell hydrogel bead with functionalized silica as the core and alginate-polyacrylamide as the shell have been developed not only to realize zero escape of engineered bacteria but also to maintain cell activity in harsh environments, such as extremely acidic/alkaline pH, high salt concentration, and strong pressure. Particularly, after combining the selective preconcentration toward pollutants by functionalized core and the positive feedback signal amplification of engineering bacteria, biosensors have realized two-stage signal amplification, significantly improving the detection sensitivity and reducing the detection limit. In addition, this strategy was actually applied to the detection of As(III) and As(V) coexisting in environmental samples, and the detection sensitivity was increased by 3.23 and 4.39 times compared to sensors without signal amplification strategy, respectively, and the detection limits were as low as 0.39 and 0.86 ppb, respectively.

Recent advances in the extraction, synthesis, biological activities, and stabilisation strategies for β‐carotene: a review

Summaryβ‐carotene is a natural carotenoid pigment that widely exists in various fruits and vegetables, possessing antioxidant, anti‐inflammatory, and other biological activities. This makes it highly suitable for the development of nutritional functional foods and cosmetics. However, its poor water solubility and physical and chemical instability hinder its actual bioavailability. Therefore, adopting a rational stabilisation strategy to improve the stability and bioavailability of β‐carotene is a feasible approach. This review provides a comprehensive overview of the properties, biological activities, extraction methods, and synthesis methods of β‐carotene. It also highlights the research progress and current applications of β‐carotene‐loaded systems with the aim to offer valuable references for developing stable systems and expanding its application scope.

Chemical processes in receiving soils accelerate solubilisation of phosphorus from desert dust and fire ash

AbstractAtmospheric deposition of desert dust and ash from wildfires are recognised as major suppliers of phosphorus (P) to soils in many terrestrial ecosystems. The biological effects of desert dust and fire ash P depend on their interactions with the receiving soils. However, the chemical processes and environmental conditions that control dust and ash P bioavailability post deposition are unknown. Soil and rhizospheric pH and organic exudates are acknowledged as central parameters that control soil P bioavailability. Here we performed a series of in‐vitro incubation experiments to study their effects on P solubility of various desert dust and fire ash samples. Then, we tested the dust and ash P solubility that were added to acidic and alkaline soils. Our results show that dust P solubility gradually increases by a few orders of magnitude as pH decreases from 7 to 2.5 and also with increased concentrations of oxalic and malic acids, two ubiquitous P solubilising organic exudates in soils. In both cases, the increase in dust P solubility occurs mainly by dissolving P from insoluble Ca‐P minerals such as apatite, the major P bearing mineral in desert dust. P solubility of fire ash was dramatically higher than that of desert dust but showed the same pattern of a gradual increase with decreasing pH or with increasing concentrations of oxalic and malic acids. When the dust was suspended with soils, extractable P level was ~10 times higher in alkaline soil than acidic soil despite the lower pH of the later, probably due to the strong P sorption capacity of the acidic soils. On the contrary, when fire ash was suspended, extractable P in the acidic soil was higher than that of the alkaline soil indicating substantial variation in P forms. Overall, our results indicate that the bioavailability of P from desert dust and fire ash is largely controlled by environmental and chemical factors in the receiving soils.Highlights Atmospheric deposition from desert dust and fire ash is a major phosphorus source to soils. However, the actual bioavailability of dust and ash P post deposition is unknown. Soil pH, organic acids concentrations and P sorption capacity controls dust and ash bioavailability. The bioavailability of atmospheric P is controlled by environmental factors in the receiving soils.

Safety of zinc l-carnosine as a Novel food pursuant to Regulation (EU) 2015/2283 and the bioavailability of zinc from this source in the context of Directive 2002/46/EC on food supplements.

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on zinc l‐carnosine as a novel food (NF) pursuant to Regulation (EU) 2015/2283 and as a source of zinc for use in food supplements. The NF is produced by chemical synthesis and is proposed to be used in food supplements as a source of zinc. The target population proposed by the applicant is individuals above the age of 12, excluding pregnant and lactating women. The NF which is the subject of the application is a chelate‐complex, formed between Zn2+ and l‐carnosine and is present as a mixture of a monomer and a dimer. The material is a powder with particulate nature and is insoluble in water at neutral pH. No relevant data using an existing zinc source as comparator have been made available by the applicant and the actual bioavailability of the zinc provided by the NF at the proposed use levels remains uncharacterised. Owing to the lack of a correct characterisation of the fraction of small particles, including nanoparticles of the NF, the Panel is not in the position to evaluate specification limits for the size of the constituent particles in the NF. Owing to the lack of information on the size distribution and the physico‐chemical properties of the particles constituting the NF, the Panel is not in the position to confirm whether the ADME studies and the toxicological studies provided by the applicant are appropriate to assess the safety of the NF. The Panel concludes that the NF is absorbed and provides zinc, but as it is in an insufficiently characterised particulate form, its safety has not been established and the bioavailability has not been determined.

Mechanistic Evaluation of the Stability of Arylvinyl-1,2,4-trioxanes under Acidic Conditions for Their Oral Administration as an Antimalarial Drug.

A mechanistic approach to understand the course of metabolism for synthetic 1,2,4-trioxanes, potent antimalarial compounds, to evaluate their bioavailability for antimalarial action has been studied in the present work. It is an important parameter to study the course of metabolism of a drug candidate molecule when administered via oral route during its journey from oral intake to its target site. From the pharmacokinetics point of view, it determines the bioavailability of an active drug or a prodrug at the target point. In this work, synthetic arylvinyl-1,2,4-trioxanes 1a–u have been evaluated under various acidic conditions to mimic the milieu of the stomach (pH between 1.5 and 3.5) through which they have to pass when administered orally. The effect of acid on trioxanes led to their degradation into corresponding ketones and glyoxal. Under such acidic conditions glyoxal polymerized to form a nonisolable condensate product. The study indicates that the actual bioavailability of the drug is far less than the administered dose.

Nutritional Quality and Safety of the Spirulina Dietary Supplements Sold on the Slovenian Market.

The microalgae Spirulina may be a popular dietary supplement rich in essential nutrients and vitamins, but oversight of the supplement industry, in general, remains limited, and increasing incidents of adulteration, misbranding, and undeclared ingredients together with misleading claims create potential risks. In response, this study characterized the elemental, amino acid and fatty acid content of commercially available Spirulina supplements in Slovenia using EDXRF, ICP-MS and GC-MS and compared the results with their nutritional declaration. The gathered data confirm that Spirulina supplements are a good source of calcium (0.15 to 29.5% of RDA), phosphorous (3.36–26.7% of RDA), potassium (0.5 to 7.69% of RDA) and selenium (0.01 to 38.6% of RDA) when consumed within recommended amounts. However, although iron contents were relatively high (7.64 to 316% of RDA), the actual bioavailability of iron was much lower since it was mainly present as the ferric cation. This study also confirms that pure Spirulina supplements are a good source of essential and non-essential amino acids, and ω-6 but not ω-3 polyunsaturated fatty acids. The presence of additives resulted in significant variation in nutrient content and, in some instances, lower product quality. Moreover, a high proportion (86.7%) of inappropriate declarations regarding the elemental content was observed. Overall, the study conclusions underline the need for a stricter control system for Spirulina-based supplements.

Extraction of selected prohealth substances from Curcuma longa and Zingiber officinale in artificial digestive juices.

The study determined the content of selected bioelements, toxic metals and phenolic acids occurring in Curcuma longa L. and Zingiber officinale Rosc. Natural raw materials in the form of powder, slices, dried and fresh rootstock, tablets and capsules were analyzed. To determine the actual bioavailability of the metals and phenolic acids present in the raw materials, they were extracted into artificial digestive juices (artificial gastric and intestinal juices). The maximum amounts of bioelements found in turmeric were as follows (mg kg-1 dry weight): Ca, 1911; Cu, 10.4; Fe, 248; K, 123; Mg, 1896; Mn, 181; Na, 332; Zn, 242. On the other hand, the maximum amounts of these bioelements found in ginger were as follows (mg kg-1 dry weight): Ca, 287; Cu, 7.4; Fe, 113; K, 2903; Mg, 1162; Mn, 11.3; Na, 1678; Zn, 186. It was found that bioelements from all the tested samples of raw materials were released to artificial digestive juices. The amount of substances extracted to digestive juices from the analyzed raw materials varied depending on their form. The highest content of bioelements was found in the fresh rhizomes of turmeric and ginger. On the other hand, powdered rhizome was characterized by the highest bioavailability of elements for humans. © 2021 Society of Chemical Industry.

Detection and quantitation of ecdysterone in human serum by liquid chromatography coupled to tandem mass spectrometry

The polyhydroxylated phytosteroid ecdysterone is present in various plants (e.g. spinach). It is widely marketed as the active component of dietary supplements, due to its reported health and performance promoting effects. For evaluation of its actual bioavailability, a fast and sensitive method was developed, optimized and validated for human serum. Instrumental analysis was performed utilizing liquid chromatography-tandem mass spectrometry with positive electrospray ionization and acquisition in multiple reaction mode. Solid phase extraction and dilute-and-inject (following protein precipitation) were tested to isolate ecdysterone from human serum. Both methods were compared in the light of the preset analytical target profile. The limit of detection (LOD) and quantitation (LOQ) for ecdysterone in human serum after SPE extraction corresponded to 0.06 ng/mL and 0.14 ng/mL, respectively, meeting the requested sensitivity of the method. The assay was linear over the range of 0.10 ng/mL to 20.83 ng/mL. As expected, the sensitivity of the SPE method was better than that of the dilute-and-inject procedure, which did not allow for quantitation of all post administration serum samples.Accuracy (relative error; %) and precision (coefficient of variation; %), were both within acceptance criteria (<15%).The developed method was successfully applied to a ten week intervention study conducted in young men performing regular resistance training. Different doses of supplements containing ecdysterone from spinach extract have been administered during the study and the quantitation of ecdysterone in serum samples has been successfully conducted. Ecdysterone could be quantified in all post-administration samples using solid phase extraction (SPE) for sample pretreatment.

Pharmacokinetic and pharmacodynamic basis for developing modified-release formulations of furosemide

Furosemide has a narrow absorption window restricted to the upper part of the gastrointestinal tract due to its ionization in the gut. Therefore, dissolution of the dose entirely in the stomach was the main aim in the development of gastroretentive extended-release dosage forms in order to sustain its delivery without losing bioavailability. Just as pharmacokinetics (PK) is a prerequisite for observing a pharmacodynamic response (PD) in the individual, the intensity of such a response could also modulate the PK of the drug whenever some physiological mechanism triggered an increase or decrease in the renal fraction of cardiac output. The urine volume increase caused by furosemide triggers the arrival of a supplementary number of molecules at the site of action, and therefore its urinary excretion rate experiences an increase in line with this new cardiac output distribution. It was found that the diuretic effect of furosemide conditioned its urinary excretion clearance. Therefore, its urinary recovery would not reflect the systemic bioavailability of formulations, but both their actual bioavailability at the biophase and their diuretic responses instead. Extended drug input yielded a more efficient diuretic response than the whole dose given rapidly, provided that drug levels at the action site were above the minimum effective concentration. A deep knowledge in the pharmacodynamics-pharmacokinetics (PD-PK) relationships is fundamental to achieve successful furosemide dosage forms. The relation between: drug excretion rates and the intensity of urine output; diuretic efficiency and drug delivery rates; and the benefit of sustained drug delivery are here analyzed. All this together leads us to conclude that the best strategy for developing gastroretentive dosage forms of furosemide would be by including two moieties within the formulation: an accelerated-release loading dose and an extended-release maintenance dose.

A method to assess bioavailability of antibiotics in anthropogenic polluted ecosystems by using a bacterial fitness test

Antibiotics released in the environment exert a selective pressure on the resident microbiota. It is well accepted that the mere measurement of antibiotics does not reflect the actual bioavailability. In fact, antibiotics can be adsorbed or complexed to particles and/or chemicals in water and soil. Bioavailable concentrations of antibiotics in soil and water are subjected to great uncertainty, therefore biological assays are increasingly recognized as that allow an indirect determination of the residual antibiotic activity. Here we propose how a fitness test for bacteria can be used to qualitatively assess the bioavailability of a specific antibiotic in the environment. The findings show that by using a pair of resistant and sensitive bacterial strains, the resulting fitness can indirectly reflect antibiotic bioavailability. Hence, this test can be used as a complementary assay to other biological and chemical tests to assess bioavailability of antibiotics.

Assessment of bioavailable B vitamin content in food using in vitro digestibility assay and LC-MS SIDA.

Standardized analytical methods, where each B vitamin is extracted from a given sample individually using separate procedures, typically ensure that the extraction conditions provide the maximum recovery of each vitamin. However, in the human gastrointestinal tract (GIT), the extraction conditions are the same for all vitamins. Here, we present an analytically feasible extraction protocol that simulates conditions in the GIT and provides a measure of the content of bioavailable vitamins using LC-MS stable isotope dilution assay. The results show that the activities of both human gastric and duodenal juices were insufficient to liberate absorbable vitamers (AV) from pure cofactors. The use of an intestinal brush border membrane (IBBM) fraction derived from the mucosal tissue of porcine small intestine ensured at least 70% AV recovery. The rate of AV liberation, however, was strongly dependent on the cofactor, e.g., in the case of NADH, it was magnitudes higher than in the case of thiamine diphosphate. For some vitamins in some food matrices, the use of the IBBM fraction assay resulted in lower values for the content of AV than conventional vitamin determination methods. Conventional methods likely overestimate the actual bioavailability of some vitamins in these cases. Graphical abstract Assessment of bioavailable B vitamin content in food.

Nano zinc, an alternative to conventional zinc as animal feed supplement: A review.

The uniqueness of Zn is that, it is the second most abundant trace element in the animal body but can't be stored in the body, thus regular dietary intake is required. Zinc oxide (ZnO) nanoparticles (NP) particles are being extensively used in paints, skin lotions pigments, food, electronics appliances, biological and pharmaceutical applications and many more. Zinc oxide nanoparticles are the specially prepared mineral salt having particle size of 1 to 100 nm. It promotes growth can act as antibacterial agent, modulates the immunity and reproduction of the animals. Both in lower and higher doses of specifications it has exhibited a variety of effects on animal performances. Apart from being highly bio-available, reports have already pointed out the growth promoting, antibacterial, immuno-modulatory and many more effects of nano zinc (nZn). These can be used at lower doses and can provide better result than the conventional Zn sources and indirectly prevents environmental contamination also. The toxicological studies provide mixed results in animal models. Studies been undertaken in diversified animal species and encouraging effects have been reported with nZn supplementation. However, there is a need to optimize the dose and duration of ZnO NP supplementation for human and livestock, depending on its biological effects. Actual bioavailability of ZnO NP in livestock is still to be worked out. In this review we have attempted to summarize, conclude the beneficial effects of nZnO and its possible usage as mineral supplement to different categories of human and livestock.

Modifications of the Method for Calculating Absolute Drug Bioavailability.

Absolute bioavailability (F) is calculated as the ratio of the area under the plasma drug concentration-time curve (AUC) between extravascular administration and intravenous injection. However, as distribution of a drug after intravenous administration does not reach an equilibrium in the body during the distribution phase, the plasma drug concentration at this phase does not reflect the total amount of drug in the body. The goal of this paper was to analyze the insufficiencies of the method for calculating on absolute bioavailability and to propose a modification to improve the calculation. Literature reporting absolute bioavailability published during 1983-2014 was searched for ten drug candidates. Plasma drug concentrations representing the amount of drug in the body were then calculated at each time point during the distribution phase according to the plasma drug concentration-time relationship during the elimination phase. The AUC values based on the distribution equilibrium drug concentrations following intravenous injection were 75%±11% of the actually measured drug concentrations in the literature. The absolute bioavailability values in the literature were 76%±12% of the actual bioavailability based on the AUCs from distribution-equilibrium drug concentrations. The present method underestimates the absolute drug bioavailability and should be modified to represent the data more accurately.This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Targeting Glioblastoma with the Use of Phytocompounds and Nanoparticles.

Glioblastoma multiforme (GBM) are extremely lethal and still poorly treated primary brain tumors, characterized by the presence of highly tumorigenic cancer stem cell (CSC) subpopulations, considered responsible for tumor relapse. In order to successfully eradicate GBM growth and recurrence, new anti-cancer strategies selectively targeting CSCs should be designed. CSCs might be eradicated by targeting some of their cell surface markers and transporters, inducing their differentiation, impacting their hyper-glycolytic metabolism, inhibiting CSC-related signaling pathways and/or by targeting their microenvironmental niche. In this regard, phytocompounds such as curcumin, isothiocyanates, resveratrol and epigallocatechin-3-gallate have been shown to prevent or reverse cancer-related epigenetic dysfunctions, reducing tumorigenesis, preventing metastasis and/or increasing chemotherapy and radiotherapy efficacy. However, the actual bioavailability and metabolic processing of phytocompounds is generally unknown, and the presence of the blood brain barrier often represents a limitation to glioma treatments. Nowadays, nanoparticles (NPs) can be loaded with therapeutic compounds such as phytochemicals, improving their bioavailability and their targeted delivery within the GBM tumor bulk. Moreover, NPs can be designed to increase their tropism and specificity toward CSCs by conjugating their surface with antibodies specific for CSC antigens, with ligands or with glucose analogues. Here we discuss the use of phytochemicals as anti-glioma agents and the applicability of phytochemical-loaded NPs as drug delivery systems to target GBM. Additionally, we provide some examples on how NPs can be specifically formulated to improve CSC targeting.

Extraction of Al, Cu, Fe, Mn, Ni and Zn-polyphenol complexes from black tea infusions by Amberlite resins

Metals can be present in tea infusion as ions or as complexes with endogenous bioligands naturally occurring in tea, especially with polyphenols. Their chemical form, i.e. free or metal complexes, can affect their actual bioavailability, gastrointestinal absorption and possible toxicity. The total amount of Al, Cu, Fe, Mn, Ni and Zn in black tea infusions was determined by inductively coupled plasma--atomic emission spectroscopy after mineralization and compared with their fractions occurring as polyphenol complexes, extracted using two different polymeric resins: Amberlite XAD-2 and Amberlite XAD-7. The obtained results demonstrated the suitability of Amberlite resins for the extraction of Al, Cu, Fe, Mn, Ni and Zn–polyphenol complexes from black tea infusions and for the evaluation of the actual distribution of the considered metals among different chemical species, i.e. as free metals and as polyphenol complexes.

Potential bioavailability and chemical forms of Co and Ni in the biogas process—An evaluation based on sequential and acid volatile sulfide extractions

Several previous studies reported stimulatory effects on biogas process performance after trace metal supplementation. However, the regulation of the bioavailability in relation to chemical speciation, e.g. the role of sulfide is not fully understood. The objective of the present study was to determine the effect of sulfide on chemical speciation and bioavailability of Co and Ni in lab‐scale semicontinuous stirred biogas tank reactors treating stillage. The chemical forms and potential bioavailability of Co and Ni were studied by sequential extraction, analysis of acid‐volatile sulfide (AVS), and simultaneously extracted metals. The results demonstrated that Ni was completely associated to the organic matter/sulfide fraction and AVS, suggesting low potential bioavailability. Cobalt was predominantly associated to organic matter/sulfide and AVS, but also to more soluble fractions, which are considered to be more bioavailable. Process data showed that both Co and Ni were available for microbial uptake. Although the actual bioavailability of Co could be explained by association to more bioavailable chemical fractions, the complete association of Ni with organic matter/sulfides and AVS implies that Ni was taken up despite its expected low bioavailability. It was concluded that extensive Co‐ and Ni‐sulfide precipitation did not inhibit microbial uptake of Co and Ni in the reactors.

Artificial membranes as models in penetration investigations

In vitro methods used in the research of transepidermal transport of active substances generally rely on the penetration rate of test compounds through standard membranes. Models typically used in penetration experiments are specially prepared human or animal skin samples or synthetic membranes. The objective of this study was to establish if the test results for an artificial liposome membrane can be extrapolated to determine the actual bioavailability of active substances. Tests were conducted in a side-by-side diffusion cell. As model membranes, a liquid-crystal lipid membrane (LM), phospholipid membrane (PM) and pig skin sample were used. The test compounds were eight synthetic dyes used in hair colouring products. Research findings reveal that membranes composed of lipids, identical to those present in the epidermis and forming analogical liquid-crystal structures provide a close approximation of the actual bioavailability of active substances (correlation between the results obtained for pig skin and LM was significant: R = 0.95 and R = 0.93 in the presence of a 1% Sodium dodecyl sulphate in donor system). Unlike biological membranes, intercellular cement does not contain phospholipids. The observed correlation between penetration coefficients through the PM and pig skin was not significant (R = 0.82). The experiments confirm that the PM constitutes a less credible model for the studies of transepidermal transport in real life conditions.

Soil monitoring of pentachlorophenol by bioavailability and ecotoxicity measurements

Several approaches to monitor the bioavailability and ecotoxicity of pentachlorophenol (PCP) in sterile and non sterile soils as a function of aging are reported. Porapak resins and water were used to assess the bioaccessibility and the bioavailability of PCP in soil. Aging effects were observed mainly after 240 d of aging. Actual bioavailability, measured as PCP bioaccumulation in earthworms, decreased more markedly with time. The ecotoxicological biomarker neutral red retention time (NRRT) displayed a dose dependent effect but no aging effects after exposing the earthworms to polluted soils. Nevertheless, mortality of earthworms increased after 240 d at 150 mg kg(-1) contamination. In contrast, the luminescent biosensor Pseudomonas fluorescens pUCD607 evidenced in non sterilized samples a slight reduction of ecotoxicity in time related to the degradation of the molecule. Once again, results highlight the necessity to study the fate of soil pollutants with different chemical and biological approaches. Different PCP degradation pathways and/or the different sensitivity of earthworms and bacteria could explain the different behaviours observed.

Actual bioavailability of divalproex sodium extended-release tablets and its clinical implications

Divalproex sodium extended-release dosage form (divalproex-ER) has been promoted as innovative formulation for the treatment of epilepsy and manic disorders, and for migraine headache prevention, with the advantage of being dosing once a day. Due to a significant decreasing in the peak-trough fluctuation of plasma valproic acid levels, in comparison with the twice-daily dosing of conventional delayed-release formulations (divalproex-DR), concentration-dependent side effects would be prevented. However the main constraint for divalproex-ER usage is the need to be administered in a higher daily dose, because of its lower bioavailability, in order to prevent eventual breakthrough seizures when patients are switched from the twice-daily divalproex DR regimen. Taking into account free plasma drug levels, divalproex ER/DR relative bioavailability could be assessed as low as 75% in fasting condition. In order to overcome the need of increase divalproex-ER daily dose, maintenance of the twice-daily regimen is suggested. Divalproex-ER administered every 12 hours not only increases steady state trough concentration to a higher value in comparison with divalproex-DR, avoiding inefficacy of the treatment, but also achieves the safest manner to treat patients with valproic acid because of reaching practically a plateau profile of drug levels.

Development of bioassessment‐based benchmarks for iron

Current water-quality criteria for metals typically are derived from toxicity tests with the metal dissolved in clean laboratory water. Estimating the toxicity of iron from such tests, however, is extremely difficult because of the complex solubility and toxicity characteristics of the ferrous and ferric forms of the metal in freshwater. Consequently, a criterion for dissolved iron in freshwater derived from standard laboratory bioassays may not accurately describe the actual bioavailability and toxicity of this metal. A new approach is necessary to adequately protect aquatic life from the direct (toxic) and indirect (physical) negative effects of iron. We present a novel methodology to derive bioassessment-based benchmarks for total iron. This approach involves the use of quantile regression to model the decline in maximum abundance of taxa along a gradient of increasing iron concentrations. The limiting function (e.g., 90th quantile) is used to project the iron concentration associated with a selected reduction in maximum number of organisms (e.g., 20%). The projected declines in abundance of aquatic organisms are interpreted within the larger context of biological responses to increasing levels of stress (i.e., a biological condition gradient). Projections of iron concentration associated with multiple levels of reduction are selected to establish acceptable levels of change in the various tiers of a biological community. The bioassessment-based benchmarks that we establish for total iron (0.21 and 1.74 mg/L) are based on the assumption that if ecological effects-based criteria for total iron are derived and applied, the structure and function of the aquatic community will be protected.