Impact of climate change on foodborne infections and intoxications.

Background: Temperature, precipitation, and humidity are important factors that can influence the spread, reproduction, and survival of pathogens. Climate change affects these factors, resulting in higher air and water temperatures, increased precipitation, or water scarcity. Climate change may thus have an increasing impact on many infectious diseases. Methods: The present review considers those foodborne pathogens and toxins in animal and plant foods that are most relevant in Germany, on the basis of a selective literature review: the bacterial pathogens of the genera Salmonella, Campylobacter and Vibrio, parasites of the genera Cryptosporidium and Giardia, and marine biotoxins. Results: As climate change continues to progress, all infections and intoxications discussed here can be expected to increase in Germany. Conclusions: The expected increase in foodborne infections and intoxications presents a growing public health risk in Germany.

Dereplication of Gambierdiscusbalechii extract by LC-HRMS and in vitro assay: First description of a putative ciguatoxin and confirmation of 44-methylgambierone.

Marine toxins have a significant impact on seafood resources and human health. Up to date, mainly based on bioassays results, two genera of toxic microalgae, Gambierdiscus and Fukuyoa have been hypothesized to produce a suite of biologically active compounds, including maitotoxins (MTXs) and ciguatoxins (CTXs) with the latter causing ciguatera poisoning (CP) in humans. The global ubiquity of these microalgae and their ability to produce (un-)known bioactive compounds, necessitates strategies for screening, identifying, and reducing the number of target algal species and compounds selected for structural elucidation. To accomplish this task, a dereplication process is necessary to screen and profile algal extracts, identify target compounds, and support the discovery of novel bioactive chemotypes. Herein, a dereplication strategy was applied to a crude extract of a G. balechii culture to investigate for bioactive compounds with relevance to CP using liquid chromatography-high resolution mass spectrometry, in vitro cell-based bioassay, and a combination thereof via a bioassay-guided micro-fractionation. Three biologically active fractions exhibiting CTX-like and MTX-like toxicity were identified. A naturally incurred fish extract (Sphyraena barracuda) was used for confirmation where standards were unavailable. Using this approach, a putative I/C-CTX congener in G. balechii was identified for the first time, 44-methylgambierone was confirmed at 8.6 pg cell-1, and MTX-like compounds were purported. This investigative approach can be applied towards other harmful algal species of interest. The identification of a microalgal species herein, G. balechii (VGO920) which was found capable of producing a putative I/C-CTX in culture is an impactful advancement for global CP research. The large-scale culturing of G. balechii could be used as a source of I/C-CTX reference material not yet commercially available, thus, fulfilling an analytical gap that currently hampers the routine determination of CTXs in various environmental and human health-relevant matrices.

Extraction and LC-MS/MS Analysis of Ciguatoxins: A Semi-Targeted Approach Designed for Fish of Unknown Origin.

Ciguatoxins (CTXs) are polyether marine biotoxins that can cause ciguatera poisoning (CP) after the consumption of fish or invertebrates containing sub ppb levels; concentrations that present a challenge for current extraction and analysis methods. Here, a newly developed and (partly) validated single-day extraction protocol is presented. First, the fish sample is broken-down by enzymatic digestion, followed by extraction and extract clean-up by defatting and two solid-phase extractions. Final extracts were investigated using two different CTX-analysis methods; an in vitro cytotoxicity assay (N2a-assay) and by LC-MS/MS. Validation was performed for both fillet and freeze-dried samples of snapper, parrotfish, and grouper spiked with CTX1B, 52-epi-54-deoxyCTX1B, 54-deoxyCTX1B, and CTX3C. Based on recovery rates (35-88%) and matrix effects (66-116%) determined by LC-MS/MS, the enzyme protocol is applicable to various matrices. The protocol was applied to naturally contaminated fish tissue (Lutjanus bohar) obtained during a CP incident in Germany. Several potential CTX congeners were identified by a two-tier LC-MS/MS approach (screening of sodium adducts, high-resolution or low-resolution confirmation via ammonium adducts). Inclusion of >30 known CTX congeners into the LC-MS/MS methods and single-day sample preparation make the method suitable for analysis of ciguatera suspect samples at sub ppb levels also with undisclosed CTX profiles.

Ciguatera Mini Review: 21st Century Environmental Challenges and the Interdisciplinary Research Efforts Rising to Meet Them.

Globally, the livelihoods of over a billion people are affected by changes to marine ecosystems, both structurally and systematically. Resources and ecosystem services, provided by the marine environment, contribute nutrition, income, and health benefits for communities. One threat to these securities is ciguatera poisoning; worldwide, the most commonly reported non-bacterial seafood-related illness. Ciguatera is caused by the consumption of (primarily) finfish contaminated with ciguatoxins, potent neurotoxins produced by benthic single-cell microalgae. When consumed, ciguatoxins are biotransformed and can bioaccumulate throughout the food-web via complex pathways. Ciguatera-derived food insecurity is particularly extreme for small island-nations, where fear of intoxication can lead to fishing restrictions by region, species, or size. Exacerbating these complexities are anthropogenic or natural changes occurring in global marine habitats, e.g., climate change, greenhouse-gas induced physical oceanic changes, overfishing, invasive species, and even the international seafood trade. Here we provide an overview of the challenges and opportunities of the 21st century regarding the many facets of ciguatera, including the complex nature of this illness, the biological/environmental factors affecting the causative organisms, their toxins, vectors, detection methods, human-health oriented responses, and ultimately an outlook towards the future. Ciguatera research efforts face many social and environmental challenges this century. However, several future-oriented goals are within reach, including digital solutions for seafood supply chains, identifying novel compounds and methods with the potential for advanced diagnostics, treatments, and prediction capabilities. The advances described herein provide confidence that the tools are now available to answer many of the remaining questions surrounding ciguatera and therefore protection measures can become more accurate and routine.

Long-term monitoring of sulfonamides and tetracyclines in manure amended soils and leachate samples - A follow-up study.

Antibiotics can be detected in manure and digestate samples worldwide. As manure is a frequently used fertilizer, antibiotics are found in soil and leachate samples. Only little is known about the long-term fate of antibiotics in the soil environment. One shortcut is the lack of appropriate monitoring studies. Here we present the results of an unequalled soil monitoring study over 18 years from an agricultural field site in Lower Saxony (Germany). Sulfonamides and tetracycline are mainly fixed in the upper soil layer. Contents showed a sharp decrease below sampling depth of 30 cm (plough depth). Sulfaguanidine and sulfamethazine (SMZ) were detected down to 90 cm. Water samples taken below the field site revealed the transfer of sulfonamides into leachate. High variances were observed between sampling points emphasizing the need for sampling strategies for environmental studies. In addition, field lysimeters with defined input of sulfonamides enabled a long-term monitoring and mass balance of antibiotic transfer into leachate over 10 years. SMZ showed the highest mobility with concentrations up to 65 ng L-1. Less than 0.5% of the applied SMZ was transferred into the leachate. Data of lysimeter and field water samples support the theory of a steady state process with a continuous input of sulfonamides such as SMZ into leachate. Soils contaminated with antibiotics can be a long-term source for the input of antibiotic active compounds into deeper soil layers and groundwater.

Degradation and transformation of fluoroquinolones by microorganisms with special emphasis on ciprofloxacin.

Although internationally recognized as the "highest priority critically important antimicrobials," fluoroquinolones are extensively used in both human and veterinary medicine. Poor metabolism and recalcitrance of fluoroquinolones have led to their worldwide presence in municipal wastewaters as well as in manure and, consequently, in several environmental compartments. Being one of the most widely used fluoroquinolones in human medicine and, aside from that, the main metabolite of the veterinary drug enrofloxacin, ciprofloxacin is the most frequently detected fluoroquinolone in effluents of European wastewater treatment plants. Due to serious global concerns about the increasing emergence of bacterial (multi)resistances toward the highly efficient fluoroquinolones, special attention has been paid to their environmental degradation by various microorganisms. This review summarizes research on microbial transformation and degradation of fluoroquinolones with special emphasis on ciprofloxacin, presents an overview of the main ciprofloxacin biotransformation products, and takes a closer look at their biological relevance. Furthermore, own data, experiences, and publications gathered from our recent research in the field are acknowledged.

Abiotic transformation products of tetracycline and chlortetracycline in salt solutions and manure.

Tetracyclines belong to the group of the most applied antibiotics in veterinary medicine worldwide. Due to their incomplete absorption and/or metabolism in the animal gut, tetracyclines are frequently detected in manure samples. Within the matrix, an elimination of these compounds has been reported in several studies. However, only little information about potential transformation products of tetracyclines in manure and the environment is available. Therefore, the fate of tetracycline (TC) and chlortetracycline (CTC) was investigated in aqueous solutions and manure. Abiotic incubation of TC in phosphate buffer led to a remarkable red-brown coloring of the solution. Subsequent compound isolation and structure elucidation by MS/MS and NMR techniques revealed the formation of seco-cycline A, a compound formerly described as a fungal biotransformation product of TC. For CTC, two comparable products were identified which were derived from its isomeric form isoCTC. All transformation products showed no antimicrobial activity for concentrations up to 500 mg L-1. When TC and CTC were incubated in cow manure for 7 d, the above mentioned three transformation products were also formed in this complex matrix (up to 5.1 mg kg-1). Manure, soil and leachate samples from Lower Saxony revealed the presence of seco-cycline A in manure and soil, but not in water. To obtain a better insight in the fate of tetracyclines in environmental matrices, future analytical and ecotoxicological studies dealing with this subject should include the analysis especially of seco-cycline A.

High-throughput analysis of insecticides on malaria vectors using liquid chromatography tandem mass spectrometry.

BACKGROUND: Different setups and protocols have been developed for investigating insecticide effects on Anopheles (An.) mosquitoes, vectors of malaria. However, chemical uptake resulting from their tarsal contact with insecticide-treated material has seldom been investigated. To address the challenges encountered in the interpretation of bioassay data, a high throughput method for chemical analysis on malaria vectors was developed and validated for five selected insecticides including alpha-cypermethrin (aCYP), deltamethrin (DM), etofenprox (EPX), permethrin (PM), pirimiphos-methyl (PPM). METHODS: The method includes a single chemical extraction step via an ultrasound probe on mosquito samples and analysis via liquid chromatography coupled to high-resolution tandem mass spectrometry (UHPLC-MS/MS). The protocol was established for two malaria vector species, Anopheles gambiae senso stricto (s.s.) and An. stephensi, both males and females. Recovery rates ranged from 70 to 100% without any influence of sex or species. The method was efficiently applied to female An. gambiae s.s. of the KISUMU1 reference strain, after susceptibility tests using the World Health Organization's standard protocol. RESULTS: Susceptibility tests revealed 13.4-18.4 minutes knockdown times for 50% mosquitoes during exposure to EPX and pyrethroids. The mortality rates 24 hours post-exposure to insecticides were mostly 99-100%, except in two PM and three PPM assays suggesting possible or confirmed resistance to these insecticides. The mean insecticide uptake in dead mosquitoes ranged from 23 pg (aCYP) to 1812 pg (EPX) per specimen. However, the mean uptake in survivors to PM and PPM was reduced by at least 25%, suggesting that acute doses were not achieved in these specimens during bioassays. CONCLUSIONS: The developed and validated UHPLC-MS/MS method could be used to address some limitations of bioassays or to assess the penetration of insecticides in mosquito matrix with reference to cuticle thickness and other insecticide resistance mechanisms.

Enrichment of vitamin D2 in mycelium from submerged cultures of the agaric mushroom Pleurotus sapidus.

Ergosterol, a precursor of vitamin D2, is present in the cell membrane of all fungi. It can be transformed into vitamin D2 by UV-B exposure. In this study, a basidiomycete, Pleurotus sapidus, cultivated in liquid malt extract medium was exposed to UV-B light. In addition, autoclaved, abiotic mycelium was put through UV-B exposure for the first time. The effects of different UV-B exposure times, surface areas and temperatures on vitamin D2 formation were analyzed. The conversion of ergosterol to vitamin D2 at ambient temperature almost reached completion within 10 min resulting in vitamin D2 concentrations of 365 µg (g dry matter)-1. Prolonged exposure of the biotic mycelium for up to 60 min resulted in a reduced vitamin D2 concentration with stagnation at about 280 µg (g dry matter)-1. Exposure of the abiotic mycelium showed a slower increase but also leveled off at the same concentration. Furthermore, it could be shown that vitamin D2 formation depends on the temperature and the exposed surface area. The vitamin D2 concentration augmented after increasing the exposed surface from 65.0 to 298.6 cm2. The ergosterol content of P. sapidus was analyzed in a way similar to vitamin D2 and resulted in 3.75 ± 0.06 mg (g dry matter)-1 ergosterol.

Biotransformation of ciprofloxacin by Xylaria longipes: structure elucidation and residual antibacterial activity of metabolites.

The impressive ability of the fungus Xylaria longipes to transform the highly persistent fluoroquinolone ciprofloxacin into microbiologically less active degradation products was demonstrated. Fluoroquinolones are used extensively in both human and veterinary medicine. Poor metabolization and high chemical stability of these synthetic antibiotics led to their presence in several environmental compartments. This undesirable behavior may promote the spread of resistance mechanisms due to concomitant exposure to bacteria. Therefore, the biotransformation of ciprofloxacin, one of the most prescribed fluoroquinolones in human medicine, by the ascomycetous soft rot fungus X. longipes was investigated in detail. Submerged cultivation of the fungus allowed for high-yield formation of four biotransformation products. These compounds were subsequently purified by preparative high-performance liquid chromatography. Applying accurate mass spectrometry and nuclear magnetic resonance spectroscopy, desethylene-ciprofloxacin, desethylene-N-acetyl-ciprofloxacin, N-formyl-ciprofloxacin and N-acetyl-ciprofloxacin were unambiguously identified. N-acetylation and N-formylation of the drug led to a 75-88% reduction of the initial antibacterial activity, whereas a breakdown of the piperazine substituent resulted in almost inactive products. These findings suggest an important role in the inactivation and degradation of this and other synthetic compounds in the environment.

Efficient Reduction of Antibacterial Activity and Cytotoxicity of Fluoroquinolones by Fungal-Mediated N-Oxidation.

Extensive usage of fluoroquinolone antibiotics in livestock results in their occurrence in manure and subsequently in the environment. Fluoroquinolone residues may promote bacterial resistance and are toxic to plants and aquatic organisms. Moreover, fluoroquinolones may enter the food chain through plant uptake, if manure is applied as fertilizer. Thus, the presence of fluoroquinolones in the environment may pose a threat to human and ecological health. In this study, the biotransformation of enrofloxacin, marbofloxacin, and difloxacin by the fungus X. longipes (Xylaria) was investigated. The main metabolites were unequivocally identified as the respective N-oxides by mass spectrometry and nuclear magnetic resonance spectroscopy. Fungal-mediated N-oxidation of fluoroquinolones led to a 77-90% reduction of the initial antibacterial activity. In contrast to their respective parent compounds, N-oxides showed low cytotoxic potential and had a reduced impact on cell proliferation. Thus, biotransformation by X. longipes may represent an effective method for inactivating fluoroquinolones.

Long-term monitoring of sulfonamide leaching from manure amended soil into groundwater.

Veterinary antibiotics such as sulfonamides are frequently applied in livestock farming worldwide. Due to poor absorption in the animal gut and/or reversible metabolization sulfonamides are excreted in considerable amounts and can subsequently be detected in liquid manure. As manure is utilized for soil fertilization, sulfonamides can enter the environment via this pathway. Water samples taken below an agriculture field in Lower Saxony revealed the permanent entrance of sulfamethazine into groundwater and concentrations up to 100 ng L-1 were determined. During a long-term lysimeter study, nine sulfonamides were applied to two different soil types by using fortified liquid manure. Divert mobilities were found with sulfamethazine und sulfamethoxazole showing the highest detection frequency in water samples taken below both bedrock and sandy soil. Four years after the last application of fortified manure, sulfonamides were still detectable in the leachate. Based on analyses of manure and fermentation residue samples, a permanent input of sulfonamides to the soil can be excluded. Thus, the positive findings must be caused by the antibiotics once applied. Soils fertilized with manure contaminated with sulfonamides can consequently be a long-time source for the transfer of antibiotics into groundwater.

Transformation of Sulfonamides and Tetracyclines during Anaerobic Fermentation of Liquid Manure.

Liquid manure is frequently used as soil fertilizer due to its high nutrient content. It can also contain residues of pharmaceuticals, such as antibiotics, if farm animals are medicated. The anaerobic fermentation process in biogas plants is discussed as one way to reduce the input of antibiotics into the environment. Therefore, 10 worldwide-applied sulfonamides (sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfaguanidine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfamethoxypyridazine, sulfapyridine, and sulfathiazole) and four frequently used tetracyclines (chlortetracycline, doxycycline, oxytetracycline, and tetracycline) were investigated concerning their elimination pattern during anaerobic fermentation. Batch fermenters with autoclaved and non-autoclaved inoculum were utilized to distinguish between biotic and abiotic elimination pathways. Overall, sulfadimethoxine, sulfamethoxypyridazine, and sulfamethoxazole showed the highest elimination, which was considerably reduced by autoclaving before inoculation. Structure elucidation via nuclear magnetic resonance and different mass spectrometry techniques revealed only minor structural modifications such as O-demethylation and hydrogenation, which did not result in a considerably reduced antimicrobial activity. These results show that, especially, sulfonamides are more persistent than expected. Future studies should deal with the elucidation of relevant process parameters for an enhanced compound degradation.

Biotransformation of Dimethenamid-P by the basidiomycete Irpex consors.

Twenty-nine basidiomycetes were screened in surface and liquid cultures for their capability to biotransform the chloroacetamide herbicide Dimethenamid-P (DMTA-P). The basidiomycete Irpex consors converted 70% of the herbicide (0.5 g L-1 DMTA-P) in liquid cultures within 6 days, applying a minimal medium under non-ligninolytic conditions. Nine transformation products of DMTA-P were identified by liquid chromatography-mass spectrometry analysis of the culture supernatants. The four main metabolites were isolated and subjected to GC-MS analysis and NMR spectroscopy. The analyses revealed that the thiophene ring was oxidized at three different positions. Metabolite M1 was identified as the S-oxide, which was isolable and relatively stable at room temperature. In metabolite M2, one methyl substituent of the thiophene ring was hydroxylated. The two metabolites M3A and M3B were diastereomers, but fully separated by HPLC. Here, oxidation of the aromatic CH carbon resulted in prototropic rearrangement to an αß-unsaturated thiolactone. None of the three major metabolites of DMTA-P has been described before.

Elimination patterns of worldwide used sulfonamides and tetracyclines during anaerobic fermentation.

Antibiotics such as sulfonamides and tetracyclines are frequently used in veterinary medicine. Due to incomplete absorption in the animal gut and/or unmetabolized excretion, the substances can enter the environment by using manure as soil fertilizer. The anaerobic fermentation process of biogas plants is discussed as potential sink for antibiotic compounds. However, negative impacts of antibiotics on the fermentation process are suspected. The elimination of sulfadiazine, sulfamethazine, tetracycline and chlortetracycline in semi-continuous lab-scale fermenters was investigated. Both biogas production and methane yield were not negatively affected by concentrations up to 38 mg per kg for sulfonamides and 7 mg per kg for tetracyclines. All substances were partly eliminated with elimination rates between 14% and 89%. Both matrix and structure of the target molecule influenced the elimination rate. Chlortetracycline was mainly transformed into iso-chlortetracycline. In all other cases, the elimination pathways remained undiscovered; however, sorption processes seem to have a negligible impact.

Biotransformation of the Antibiotic Danofloxacin by Xylaria longipes Leads to an Efficient Reduction of Its Antibacterial Activity.

Fluoroquinolones are considered as critically important antibiotics. However, they are used in appreciable quantities in veterinary medicine. Liquid manure and feces can contain substantial amounts of unmetabolized antibiotics and, thus, antibiotics can enter the environment if manure is used for soil fertilization. In this study, the microbial biotransformation of the synthetic veterinary fluoroquinolone danofloxacin by the ascomycete Xylaria longipes was investigated. Fungal submerged cultures led to a regioselective and almost quantitative formation of a single metabolite within 3 days. The metabolite was unequivocally identified as danofloxacin N-oxide by high-resolution mass spectrometry and one- and two-dimensional nuclear magnetic resonance spectroscopic techniques. An oxidation of the terminal nitrogen of the substituted piperazine moiety of the substance led to a remarkable reduction of 80% of the initial antibacterial activity. Thus, fungal enzymes involved in the biotransformation process might possess the potential to reduce the entrance of antibiotics via biotransformation of these compounds.

Simultaneous determination of 14 sulfonamides and tetracyclines in biogas plants by liquid-liquid-extraction and liquid chromatography tandem mass spectrometry.

A new method for the analysis of sulfonamides and tetracyclines in heterogenic biogas plant input samples and fermentation residues is introduced. Veterinary antibiotics are only partially absorbed in the animal gut; therefore, animal manure can contain high loads of these substances. Animal manure is used for biogas generation, so antibiotics can enter the anaerobic fermentation process this way. However, only little is known about the fate of antibiotics within this process, also due to the lack of suitable analytical methods for this complex sample matrix. Therefore, we developed a method for the analysis of ten sulfonamides (sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfaguanidine, sulfamerazine, sulfamethazine, sulfamethoxazol, sulfamethoxypyridazin, sulfapyridine, sulfathiazole) and four tetracyclines (chlortetracycline, doxycycline, oxytetracycline, tetracycline) in biogas plant input and output samples, including a single liquid-liquid-extraction step and analysis via liquid chromatography (LC) and triple quadrupole mass spectrometry. The detection limit of this method ranges from 0.01 to 0.08 mg kg(-1). Matrix calibration using antibiotic-free cattle feces and isotopic-labeled internal standards enables quantification of antibiotics in different matrices such as animal manure, dung, or fermenter outputs with recovery rates between 70 and 130 %. This makes the method suitable for investigating the fate of antibiotics in animal manure and fermentation processes. A screening of 15 German biogas plants revealed the presence of several antibiotics up to 9 mg kg(-1) (201 mg kg(-1) dry matter). During the fermentation process, elimination occurs; however, with the exception of chlortetracycline, the antibiotic content remains in the same order of magnitude.

Influence of temperature and elevated carbon dioxide on the production of dimethylsulfoniopropionate and glycine betaine by marine phytoplankton.

The sulfur metabolite dimethylsulfoniopropionate (DMSP) is the most important precursor of the climate relevant metabolite dimethylsulfide (DMS). It has thus gained interest in the context of climate change and several studies investigated the influence of elevated temperature and/or CO(2) on DMSP in complex plankton communities. However, only little information about changes in response to these factors in single species is available. Therefore, we analyzed DMSP in different phytoplankton cultures (Thalassiosira pseudonana, Phaeodactylum tricornutum, Emiliania huxleyi) under the influence of increased temperature by 6 °C and elevated CO(2) to 790 ppmv. In addition, we addressed glycine betaine (GBT) that fulfills a similar function as osmolyte like DMSP. In all cultures GBT concentrations increased at higher temperature and decreased at elevated CO(2). In contrast, diatoms and prymnesiophytes revealed opposite trends for DMSP. In diatoms increased CO(2) and temperature led to decreased DMSP concentrations, while rather elevated levels of this metabolite under the influence of these parameters were observed for E. huxleyi.

Investigations of the uptake of dimethylsulfoniopropionate by phytoplankton.

No change here: Analysis with doubly labeled [(13)C(2)D(6)]DMSP and LC/MS revealed that dissolved DMSP is taken up and stored intracellularly by diverse phytoplankton species without transformation. This is even true for species that produce no quantifiable amounts of DMSP themselves.

Direct quantification of dimethylsulfoniopropionate (DMSP) with hydrophilic interaction liquid chromatography/mass spectrometry.

A simple, derivatization free method for the direct determination of dimethylsulfoniopropionate (DMSP) using hydrophilic interaction liquid chromatography (HILIC)/mass spectrometry is introduced. DMSP is a zwitterionic osmolyte which is produced from marine plankton, macro algae and higher plants. Due to its central role in climate relevant geochemical processes as well as in plant physiology and chemical ecology there is a great interest in methods for its quantification. Since DMSP is labile and difficult to extract currently most protocols for quantification are based on indirect methods. Here we show that ultra performance liquid chromatography/mass spectrometry using a HILIC stationary phase is suitable for the direct quantification of DMSP from aqueous samples and microalgal extracts. The protocol requires minimal sample preparation and phytoplankton samples can be investigated after filtration of small volumes. The limit of detection is 20nM and the calibration curve is linear in the range of 60nM to 50µM. The use of [(2)H(6)]-DMSP as internal standard allows prolonged sample storage since it is transformed with the same kinetics as natural DMSP. This makes the method suitable for both laboratory and field studies.