Toxicological and ecological implications of biotransformation enzymes in the tropical teleost Chaetodon capistratus

Hepatic cytochromes P450 (phase I monooxygenases) and glutathione transferases (phase II conjugating enzymes) were investigated in Chaetodon capistratus (Linnaeus) collected in Florida and Belize in June and December 1991, respectively. These biotransformation enzymes play major roles in the detoxification of xenobiotics by converting lipophilic chemicals to more hydrophilic, readily excretable metabolites. Content of total microsomal P450 (0.501 to 0.821 nmol mg^-1 microsomal protein) and rates of NADPH-cytochrome c (P450) reductase (270.7 to 330.2 nmol min^-1 mg^-1 microsomal protein) and glutathione transferase (2.81 to 3.12 g min^-1 mg^-1 cytosolic protein) in these fish were greater than in most untreated fish species, i.e., fish that have not been exposed to PAHs (polycyclic aromatic hydrocarbons) or PCBs (polycyclic biphenyls). Ethoxyresorufin O-deethylase (EROD) rates (0.029 to 0.171 nmol min^-1 mg^-1) were also comparable to those in most untreated marine fish. Immunoblot analysis with monoclonal antibody (MAb) 1-12-3 to scup P450E (the EROD catalyst and a teleost representative of the PAH-inducible CYP1A gene subfamily) showed slight amounts of cross-reacting protein in C. capistratus liver microsomes. Hepatic CYP1A content and EROD activity did not differ significantly between fish collected in Florida and Belize, suggesting that the two sites differed little in contamination by CYP1A inducers. Immunochemical analyses with polyclonal antibodies to scup P450B (a teleost representative of the CYP2B subfamily) and human CYP3A4 cross-reacted strongly with C. capistratus hepatic proteins. The CYP2B and CYP3A subfamilies in mammals are believed to have partially evolved in response to toxic dietary allelochemicals. C. capistratus regularly feeds on terpenoid-rich gorgonian corals, suggesting that biotransformation enzymes may be involved in the metabolism of dietary allelochemicals as well as anthropogenic xenobiotics in this species.     

Research progress in microbial cytochrome P450 and xenobiotic metabolism北大核心CSCD

Cytochrome P450 (CYP450s) is a type of heme-mercaptide protein superfamily, which is distributed widely in animals, plants, and microorganisms. CYP450s can oxidize and degrade many exogenous compounds such as drugs, herbicides, pesticides, some persistent organic pollutants, and so on. Based on recent researches, this paper reviews the nomenclature, classification, structure, and catalytic mechanism of P450 enzymes, and summarizes the research progresses in the metabolism and biodegradation of xenobiotics using P450 enzymes from microorganisms. The nomenclature and classification of the P450 gene superfamily mainly rely on the similarities of amino acid sequences. Although the structures of P450 are conserved, their recognition sites towards to the substrates are variable. This is also the structural basis for the catalytic diversities of P450 enzymes. Few P450 enzymes from bacteria and fungi can metabolize and degrade xenobiotics such as polycyclic aromatic hydrocarbons, herbicides, and so on. However, these P450 enzymes are less likely be used in practical applications because of their low catalytic activities. In the future, more P450 enzymes with high degradable efficiencies towards xenobiotics are needed to be obtained using multiple omics tools or modifying the existing P450 enzymes, to achieve the bioremediation of the environment. © 2018 Science Press. All rights reserved.     

Responses of the flea beetles Phyllotreta nemorum and P. cruciferae to metabolically engineered Arabidopsis thaliana with an altered glucosinolate profile

Summary. Insects feeding on Cruciferae recognize their host plants at least partially by means of specific responses to glucosinolates. However, the effects of variations in glucosinolate levels on the acceptability of plants for specialized insects are not well understood. A survey of the literature demonstrated positive, no, as well as negative correlations between plant acceptability and glucosinolate levels. The present study took advantage of the presence of transgenic Arabidopsis thaliana plants with increased glucosinolate levels. Transgenic A. thaliana contain the CYP79A1 gene from Sorghum bicolor. This gene encodes an enzyme which converts L-tyrosine into p-hydroxyphenylacetaldoxime in the biosynthesis of cyanogenic glycosides in S. bicolor. In transgenic A. thaliana plants, endogenous enzymes convert p-hydroxyphenylacetaldoxime into p-hydroxybenzylglucosinolate (sinalbin), which is not found naturally in this plant. The introduction of CYP79A1 resulted in a four-fold increase in total glucosinolate levels in transgenic A. thaliana plants. Although these changes in glucosinolate levels were rather dramatic, they did not have any effects on the acceptability of A. thaliana for the two flea beetle species, Phyllotreta nemorum and P. cruciferae. The flea beetles did not discriminate between transgenic and wildtype plants. Furthermore, they did not discriminate between leaf discs of wildtype plants where different concentrations of p-hydroxybenzylglucosinolate had been applied topically on the leaf surface. Feeding in P. nemorum was stimulated by extremely high levels of allylglucosinolate while this compound had no effect on P. cruciferae. It is concluded that the effect of glucosinolates on adapted insects depends on the chemical or physical environment in which the glucosinolates are found.     

Cytochrome P450 monooxygenase specific activity reduction in wheat <Emphasis Type="Italic">Triticum aestivum</Emphasis> induced by soil roxithromycin stress

Roxithromycin, as widely used medicine and livestock growth promoter, arouses concern because its occurrence and persistence in soil environments. However, effects of roxithromycin in higher plants are still vague. Accordingly, we hypothesized that roxithromycin-contaminated soil may exhibits ecotoxicological effects in wheat (Triticum aestivum). In this study, effects induced by a gradient concentration of roxithromycin stress (0.01, 0.1, 1, 10, and 100 mg·kg^–1) was investigated in a 7-d soil test in T. aestivum. Results indicated that the specific activity of cytochrome P450 (CYP450) monooxygenase was decreased dramatically with the concentration of roxithromycin in soil. The IC₅₀ value was 8.78 mg·kg^–1 of roxithromycin. On the contrary, the growth related endpoints (i.e., the germination percentage, the biomass and the height), the content related endpoints (i.e., soluble protein content and CYP450 content), and the superoxide dismutase (SOD) activity failed to reveal the roxithromycin-induced effects. Further analysis revealed that the CYP450 monooxygenase specific activity reduction was enzymatic mechanism mediated, other than oxidative stress induced. We conclude that the soil roxithromycin declined the CYP450 monooxygenase activity in T. aestivum by the inhibition of the enzymatic mechanism. Further efforts can include, but are not limited to, investigation of joint effects induced by combined exposure of roxithromycin and the pesticides and evaluation of the similar effects in other higher plants.     

Nutzung der induzierbaren Genexpression des NematodenCaenorhabditis elegans als Biomonitor

The soil nematodeCaenorhabditis elegans is one of the simplest animals having the status of a laboratory model. Its already completely sequenced genome contains the remarkable number of 80 cytochrome P450 genes (CYP) and many further genes coding for enzymes involved in biotransformation. In order to study xenobiotically induced gene expression inC. elegans, liquid cultures were exposed to different, well-known xenobiotic inducers. The mRNA expression was detected by two different types of DNA arrays and semi-quantitative RT-PCR. β-naphthoflavone, PCB52 and lansoprazol were the most active and, in particular, induced almost all CYP35 isoforms strongly. In conclusion, the xenobiotic dependent gene expression ofC. elegans is a useful tool to reveal defense mechanisms against potential damaging substances as well as for developing a biomonitoring system.     

Mutagenicity of polyaromatic hydrocarbons by chemical models for cytochrome P450 in Ames assay

DNA damage is an important step in carcinogenesis. The Ames assay is a short-term screening of carcinogens that induce DNA damage. Most carcinogens require enzymatic activation through oxidation by cytochrome P450 (CYP450) in the presence of S9 mix. A combination of iron (Fe)(III) porphyrin and an oxidant is also able to oxidize compounds as an alternative metabolic pathway to CYP450. Previously it was reported that a chemical model containing a water-soluble 5,10,15,20-tetrakis(1-methylpyridinium4-yl)porphyrinatoiron(III) chloride (4-MPy) and tert-butyl hydroperoxide (t-BuOOH) activated aromatic amines and amides. In this study, a chemical model composed of an Fe porphyrin, water-insoluble 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinatoiron(III) chloride (F₅P) or water-soluble 4-MPy was optimized with an oxidant – t-BuOOH, magnesium monoperoxyphthalate (MPPT), or iodosylbenzene (PhIO). Subsequently the mutagenicity of benzo[a]pyrene (B[a]P) and chrysene in Salmonella typhimurium TA strains was compared. B[a]P was activated by a combination of F₅P or 4-MPy plus MPPT or PhIO in S. typhimurium TA1538. The B[a]P-induced mutagenicity with F₅P plus oxidant was higher than 4-MPy plus oxidant. Mutagenicity of chrysene, a tetracyclic aromatic hydrocarbon, was not detected in the presence of F₅P/PhIO in S. typhimurium TA98, but was activated in the presence of F₅P/MPPT. The F₅P/MPPT activated other polyaromatic hydrocarbons (PAH) in the S. typhimurium TA98 assay including dibenz[a,c]anthracene, dibenz[a,h]anthracene, 3-methylcholanthrene, and benzo[a]anthracene. The results indicated that the F₅P/MPPT was the most efficient model for detecting PAH-induced mutagenicity in the Ames assay.     

Accumulation, distribution and transformation of DDT and PCBs by Phragmites australis and Oryza sativa L.: II. Enzyme study

Two wetland plant species, Phragmites australis and Oryza sativa, were grown in a glasshouse under hydroponics conditions. Enzyme extracts from different parts of the plants were used to determine the transformation rate of o,p′-DDT, p,p′-DDT and PCBs. The organic pollutants were directly spiked into the enzyme extracts, and samples were collected every 30 min and analyzed with a GC-ECD. Root extracts of P. australis readily degraded and transformed DDT and some PCB congeners with a low degree of chlorination. In contrast, crude extracts of O. sativa showed no appreciable degradation or transformation of DDT or PCBs. Inhibition studies indicated that the degradation and transformation of both DDT and PCBs by P. australis enzymes were partly mediated by peroxidase and the plant P-450 system. PCBs with a high degree of chlorination were highly resistant to transformation or degradation by plant enzymes. Both wetland plant species accumulated substantial quantities of the persistent organic chemicals but had different degradation capacities. The enzyme systems in P. australis were much more effective that those in rice in the degradation and transformation of the organic pollutants.     

PFOS对多齿围沙蚕CYPs、GST基因转录及酶活性的毒性效应

多毛类沙蚕已经广泛应用于海洋环境污染的生物监测,但其对新型持久性有机污染物全氟辛烷磺酰基化合物PFOS的毒理学研究尚无报道。本研究以潮间带优势种多齿围沙蚕(Perinereis nuntia)为研究对象,以细胞色素P450(CYP)、谷胱甘肽硫转移酶(GST)的基因和酶作为联合指标,研究了在PFOS亚致死浓度(4、8、16 mg·L-1)暴露第1、4、7、14天及净水恢复5 d后多齿围沙蚕CYP431A1、CYP424A1基因转录水平和EROD酶活性、GST omega基因转录水平和GST酶活性的响应情况。结果表明,PFOS暴露对EROD的抑制具有明显的时间-效应关系;CYP2系成员CYP431A1基因转录水平对PFOS的响应具有良好的剂量-效应关系并在胁迫第14天表现出最高的可诱导性;CYP4系基因CYP424A1的转录在4、8 mg·L-1处理组中与PFOS暴露时间正相关。II相解毒系统成员GST酶活和GST omega基因的响应均表现出随着PFOS胁迫时间的延长先下降,后上升的规律;多齿围沙蚕在高强度PFOS胁迫下仍可加速新陈代谢,表现出对PFOS的耐受性;净水恢复阶段,各指标都有向对照组水平恢复的趋势。总之,基因和蛋白的响应表明CYPs和GST在多齿围沙蚕PFOS新陈代谢中发挥重要作用,这些基因和酶具有作为生物标志物监测海洋潮间带PFOS污染效应的潜力。     

Metabolic fate of aromatic amines in the mussel Mytilus galloprovincialis

The postmitochondrial fraction of the digestive gland from the marine mussel Mytilus galloprovincialis possesses FAD-containing monooxygenase (EC 1.14.38) but lacks cytochrome P-450 dependent benzo(a)pyrene monooxygenase (EC 11.4.14.1). This is also evidenced by the ability of the mussel preparation to activate carcinogenic aromatic amines, but not carcinogenic benzo(a)pyrene, to Salmonella typhimurium TA 98 mutagens. This metabolic activity is NADPH dependent. Mussel digestive gland postmitochondrial fraction also possesses the enzymes needed for the detoxicating part of the aromatic amine metabolism: UDP-glucuronyl transferase (EC 2.4.1.17) and -glucuronidase (EC 3.2.1.31). Under the experimental conditions used here, this aromatic amine metabolic pathway converts up to 8% of 2-acetylamino(9-¹⁴C)fluorene, but not (G-³H)benzo(a)pyrene, to water soluble glucuronides. Glucuronic acid stimulates the formation of these glucuronides. The metabolites liberated from these glucuronides by the -glucuronidase treatment could be converted to TA 98 strain mutagens by the carp liver postmitochondrial fraction, but not by the mussel's digestive gland preparation. The presence of such a selective potential for the bioactivation and detoxication of aromatic amines, and not polycyclic aromatic hydrocarbons, in the marine invertebrate(s) may bring new insight to our understanding of the effects and the fate of carcinogens in the marine environment.     

Edible wild plants growing in contaminated floodplains: implications for the issuance of tribal consumption advisories within the Grand Lake watershed of northeastern Oklahoma,USA

Metal releases from the Tri-State Mining District (TSMD) that is located in southwestern Missouri, southeastern Kansas, and northeastern Oklahoma, have contaminated floodplain soils within the Neosho and Spring river watersheds of the Grand Lake watershed. Since the Oklahoma portion of the watershed lies within ten tribal jurisdictions, the potential accumulation of metals within plant species that are gathered and consumed by tribal members, as well as the resulting metal exposure risks to tribal human health, was a warranted concern for further investigation. Within this study, a total of 36 plant species that are commonly consumed by tribes were collected from floodplain areas that were previously demonstrated to have elevated soil metal concentrations relative to reference sites. A significant, positive correlation was shown for metal concentrations in plant tissues versus soil (n = 258; Cd: R = 0.72, p = 0.00; Pb: R = 0.52, p = 0.00; and Zn: R = 0.70, p = 0.00). Additionally, a significant difference in metal concentration distributions existed between reference and impacted plant samples (n = 210, p = 0.00 for all metals). These results proved that floodplain soils are a major contamination pathway for metal accumulation within plants, and the source of metal contamination is the result of mining releases from the TSMD. Metal accumulation within plants was found to vary according to specific metal and plant species. The lowest dietary exposure out of all plant organs sampled were associated with fruit, whereas the highest was associated with roots, stem/leaves, and low-lying leafy greens. Metals in plants were compared to weekly dietary intake limits established by the Joint FAO/WHO Expert Committee on Food Additives. Based on specific serving sizes established within this study for tribal children and adults, many plant species had sufficient concentrations to warrant tribal consumption restrictions within the floodplains of Elm Creek, Grand Lake, Lost Creek, Spring River, and Tar Creek. Importantly, these results highlighted the necessity for the issuance of plant consumption advisories for tribal communities in the watershed. A consumption restriction guide on the number of allowable servings of each species per week at specific streams was developed within this study for tribal children and adults. Results also demonstrated that soil metal concentrations do not need to be exceptionally elevated relative to reference sites in order for plants to accumulate sufficient metal concentrations to exceed dietary limits for one serving. Therefore, the exposure risk associated with the consumption of plants cannot be accurately predicted solely from metal concentrations within soils, but must be based on metal concentrations within specific plant tissues on a site-by-site basis. A weekly consumption scenario was created within this study in order to better understand the potential metal dietary exposures to child and adult tribal members who consume multiple servings of multiple plant species per day, as well as benthic invertebrates and fish from the watershed. These findings demonstrated that plants pose a greater consumption exposure risk for tribal members than benthic invertebrates or fish. Therefore, without the consideration of exposure risks associated with the consumption of plants within future human health risk assessments, tribal health risks will be severely underestimated.     

Balkan endemic nephropathy and aristolochic acid I: an investigation into the role of soil and soil organic matter contamination,as a potential natural exposure pathway

Aristolochic acids (AAs) are carcinogenic and nephrotoxic plant alkaloids present in Aristolochia species, used in traditional medicine. Recent biomolecular and environmental studies have incriminated these toxins as an etiological agent in Balkan endemic nephropathy (BEN), a severe kidney disease occurring in the Balkan Peninsula. The questions on how the susceptible populations are exposed to these toxins have not yet been clearly answered. Exposure to AAs through the food chain, and environmental pollution (soil/dust), could provide an explanation for the presence of BEN in the countries where no folkloric use of the plant has been documented (Bulgaria, Croatia). Additional exposure pathways are likely to occur, and we have shown previously that AAs can contaminate crop plants through absorption from soil, under controlled laboratory environment. Here, we attempt to provide additional support to this potential exposure pathway, by revealing the presence of AAI in soil and soil organic matter samples collected from BEN and non-BEN areas. The samples were processed in order to be analyzed by high-pressure liquid chromatography, and ion trap mass spectrometry. Our results showed the presence of AAI in small concentrations, both in BEN and non-BEN soils, especially where Aristolochia plants and seeds were present.     

Bioassay zur Bestimmung von TCDD-Toxizitätsäquivalenten (TEQ) von Umweltproben und Reststoffen

Polychlorinated aromatic hydrocarbons (HAH) like 2,3,7,8-tetrachloro-p-dioxin (TCDD) elicit a multitude of toxic and biological effects. A common trait of these substances is their affinity for a cytosolic receptor protein and the subsequent induction of the synthesis of several gene products, including cytochrome P450 1A1 (CYP 1A1). In this publication we present a bioassay to determine the induction of CYP 1A1 as a sum parameter for the total toxic potential of critical halogenated compounds in complex environmental matrices. In order to eliminate compounds like polycyclic aromatic hydrocarbons (PAH) and naturally occurring substances which might interfere with the bioassay we developed a simple cleanup procedure. TEQ values derived from bioassay are in good agreement with those obtained from chemical analysis. This bioassay in combination with the simplified “single column” clean up represents a cost and time effective alternative to chemical analysis for the screening of large numbers of environmental matrices.     

The influence of metabolically engineered glucosinolates profiles in Arabidopsis thaliana on Plutella xylostella preference and performance

The oviposition preference and larval performance of the diamondback moth (DBM), Plutella xylostella, was studied using Arabidopsis thaliana plants with modified glucosinolate (GS) profiles containing novel GSs as a result of the introduction of individual CYP79 genes. The insect parameters were determined in a series of bioassays. The GS content of the plants as well as the number of trichomes were measured. Multivariate analysis was used to determine the possible relationships among insect and plant variables. The novel GSs in the tested lines did not appear to have any unequivocal effect on the DBM. Instead, the plant characteristics that affected larval performance and larval preference did not influence oviposition preference. Trichomes did not affect oviposition, but influenced larval parameters negatively. Although the tested A. thaliana lines had earlier been shown to influence disease resistance, in this study no clear results were found for P. xylostella.     

Expression and regulation of the shikimic acid pathway gene DHD/SDH in tea plant (Camellia sinensis)北大核心CSCD

3-Dehydroquinic acid dehydrase/shikimate dehydrogenase (DHD/SDH) is the only bifunctional enzyme in the shikimic acid pathway. It can catalyze the generation of shikimic acid and gallic acid. To investigate the expression and regulation patterns of DHD/SDH in tea, we aimed to determine (1) the miRNA-mediated cleavage of DHD/SDH involved in the shikimic acid pathway, (2) the expression pattern of miRNA and their targets, and (3) the expression pattern of three DHD/SDH genes in tea plant (Camellia sinensis) with different hormone treatments via online prediction, RLM-RACE, and qPCR. Based on the miRNAs obtained, we identified four miRNAs that regulated CsDHD/SDH in tea. CsDHD/SDH2 was targeted by miR5180b, miR1510b-5p, and miR24; CsDHD/SDH3 was targeted by miR868-5p. We also found that CsDHD/SDH2 and CsDHD/SDH3 have a similar expression pattern under different hormone treatments, and they were synergistic with each other. CsDHD/SDH1 exhibited an expression pattern opposite to that of the other two homologues, and increased expression of CsDHD/SDH1 reduced the expression of the other two genes. © 2018 Science Press. All rights reserved.     

Impact of logging activities in a tropical mangrove on ecosystem diversity and sediment heavy metal concentrations

Productivity of mangrove ecosystems is compromised by anthropogenic activities including over-exploitation of wood. This study set out to understand how different wood harvesting regimes have affected the biodiversity of a tropical ecosystem and to identify relationships between the heavy metal concentrations in the mangrove sediments and tree felling. Soil samples were collected and plant diversity studies carried out on seven sites in the mangrove. Physico-chemical, chemical and mineralogical analyses were done on soil samples and plant population structure, species richness, evenness and diversity index at these sites were calculated. Results showed that soils across sites were characteristically clayey and acidic, with high organic matter content. Minerals identified included quartz, gibbsite, goethite, hematite and kaolinite. Heavy metal concentrations were higher in Sites 6 and 7 with a longer history of anthropogenic activity. There were strong negative correlations between the duration of logging and NO₃-N (r = ?0.838, p = 0.019), total N (r = ?0.837, p = 0.019), NH₄ ⁺-N (r = ?0.844, p = 0.017), Mg = (?0.789, p = 0.035), K (r = ?0.819, p = 0.024), and Na (r = ?0.988, p = 0.002). Sites which had experienced logging for longer periods (sites 3, 6, and 7) had lower nutrient content and lower values for species richness and diversity index. Logging in mangrove ecosystems could alter soil characteristics, decreasing plant diversity and abundance. Logging dynamics around mangrove ecosystems should be considered in the wider strategy for management and conservation of similar mangrove ecosystems.     

Isolation and sequence of cDNA encoding a 3-methylcholanthrene-inducible cytochrome P450 from wild red sea bream,Pagrus major

We have isolated a cDNA clone of mRNA for the cytochrome P450 from a 3-methylcholanthrene (MC)-treated red sea bream,Pagrus major, using a cDNA fragment for rat P4501A2 as a probe. The cloned cDNA is ca. 1.8 kb long and contains an open reading frame of 1545 nucleotides for polypeptides of 515 amino acids. The deduced N-terminal amino acid sequence of the cDNA is very similar to that for purified cytochrome P450 protein from the marine fish scup, which was reported previously (Klotz et al. 1983). A conserved amino acid sequence containing a putative heme-binding cysteine is present in the equivalent position proximate to the C-terminus of the molecules. The deduced amino acid sequence shows more than 50% positional identity with known members of the mammalian aromatic hydrocarbon-inducible P450 family. RNA blot analysis indicates that P450 mRNA (s) is expressed in the liver, kidney, gill and gut of the MC-treatedP. major.     

Long-term and trans-life-cycle effects of exposure to ocean acidification in the green sea urchin Strongylocentrotus droebachiensis

Anthropogenic CO₂ emissions are acidifying the world’s oceans. A growing body of evidence demonstrates that ocean acidification can impact survival, growth, development and physiology of marine invertebrates. Here, we tested the impact of long-term (up to 16 months) and trans-life-cycle (adult, embryo/larvae and juvenile) exposure to elevated pCO₂ (1,200 μatm, compared to control 400 μatm) on the green sea urchin Strongylocentrotus droebachiensis. Female fecundity was decreased 4.5-fold when acclimated to elevated pCO₂ for 4 months during reproductive conditioning, while no difference was observed in females acclimated for 16 months. Moreover, adult pre-exposure for 4 months to elevated pCO₂ had a direct negative impact on subsequent larval settlement success. Five to nine times fewer offspring reached the juvenile stage in cultures using gametes collected from adults previously acclimated to high pCO₂ for 4 months. However, no difference in larval survival was observed when adults were pre-exposed for 16 months to elevated pCO₂. pCO₂ had no direct negative impact on juvenile survival except when both larvae and juveniles were raised in elevated pCO₂. These negative effects on settlement success and juvenile survival can be attributed to carry-over effects from adults to larvae and from larvae to juveniles. Our results support the contention that adult sea urchins can acclimate to moderately elevated pCO₂ in a matter of a few months and that carry-over effects can exacerbate the negative impact of ocean acidification on larvae and juveniles.     

Appropriate pCO2 treatments in ocean acidification experiments

Experiments in which organisms are reared in treatments simulating current and future pCO₂ concentrations are critical for ocean acidification (OA) research. The majority of OA exposure experiments use average atmospheric pCO₂ levels as a baseline treatment. We conducted an ecoregion-scale analysis of global carbon chemistry datasets. For many locales, atmospheric pCO₂ levels are not an appropriate characterization of marine carbon chemistry. We argue that atmospheric pCO₂ should be disregarded when setting baseline treatment conditions and experimental design should rely on measurements of carbon chemistry in a study subject’s habitat. As carbon chemistry conditions vary with space and time, we suggest using a range of pCO₂ values as a control rather than a single value. We illustrate this issue with data on the habitat of Euphausia pacifica, which currently lives in waters with a pCO₂ around 900 μatm, a concentration much higher than the current global atmospheric mean.     

Cattle egrets as a biosentinels of persistent organic pollutants exposure

We investigated selected chlorinated pollutants (β-HCH, γ-HCH, DDDs, DDEs, o,p′-DDT, p,p′-DDT, heptachlor, aldrin, dieldrin, and endrin) in the Lahore and the Sialkot districts of Pakistan, using eggs of cattle egret (Bubulcus ibis) collected during May and June 2007. The pollutant with highest level and frequency was ΣDDT, followed by β-HCH, γ-HCH, heptachlor, aldrin, dieldrin, and endrin in descending order. The concentration(s) were significantly higher in Sialkot heronry for all the pollutants (except p,p′-DDT) than in Lahore. The values for DDTs, β-HCH, γ-HCH, and heptachlor were significantly higher (p < 0.05) in the egg(s) than in sediment(s) and in the chicks’ diet, due to biomagnification. Among DDTs analogues, p,p′-DDD was the major contaminant with >60 % of total DDT burden, reflecting the widespread aged as well as recent use of DDT as well as anaerobic degradation (DDD/DDE > 1 in many cases) in the nearby paddy soils. In few samples, p,p′-DDT/(DDD + DDE) > 0.5 suggested the recent emission patterns from surrounding contaminated areas of demolished DDT units and obsolete pesticide stores. The higher levels of HCHs (i.e., β-HCH) in the samples collected from Sialkot indicate exposure from long-term agricultural use. Overall, concentrations of all studied POPs were less than the threshold levels known to affect reproduction. Nevertheless, total DDTs and/or HCHs burdens in some eggs contained concentrations of greater than what would educe adverse effects on birds. This is among few studies on OCPs exposure to avian species, which provide the evidence of Pakistan’s contribution toward the Global POPs emission.