Distribution patterns of chalcogens (S, Se, Te, and 210Po) in various tissues of a squid, Todarodes pacificus.pdf

distribution patterns of chalcogens s se te and 210po in various tissues of a squid todarodes pacificus hannelore waskaa seolwon kima guebuem kima mi ran kangb gi beum kimb aschool of earth and environmental sciences rio seoul national university seoul 151 742 republic of korea bdepartment of marine environmental engineering marine industry institute gyeongsang national university tongyeong 650 160 republic of korea a r t i c l e i n f oa b s t r a c t article history received 17 september 2007 received in revised form 4 december 2007 accepted 4 december 2007 available online 11 january 2008 in order to elucidate the relationship between the chemically similar chalcogen elements s se te and 210po in marine invertebrates we conducted a comparative study of the distribution patterns of these elements in a squid todarodes pacificus elemental concentrations of the four chalcogens were determined in mantle muscle gill stomach and hepatopancreas tissues no relationship between chalcogen concentrations and morphological parameters mantle length body weight and sex was evident gills showed slightly elevated levels of se and 210po which may indicate absorption and uptake of these elements over the gill surface all four chalcogens have their highest concentrations in the hepatopancreas and the lowest concentrations in the muscle tissue however concentration differences between tissues revealed by 1 bioaccumulation values based on reference seawater values and 2 internal relative enrichment factors iref based on enrichment of hepatopancreas compared to muscle tissue were least pronounced for s most distinct for 210po and moderate for se and te furthermore no significant correlation for se te and 210po with s within tissue concentrations and only a slightly negative correlation between sand210po inthe squid muscle and hepatopancreas tissues were found which indicates either an antagonistic effect between or a disconnection of the two elements through metabolic processing overall the distribution patterns of se and te resemble those of essential trace elements such as zn and cu whereas 210po is partitioned in a manner similar to toxic heavy metals such as cd and ag 2007 elsevier b v all rights reserved keywords sulfur selenium tellurium polonium squid chalcogen bioaccumulation 1 introduction four elements of the chalcogen group s se te and 210po have similar chemical properties according to their position in the periodic table but different functions in the living organism barceloux 1999 chasteen and bentley 2003 moroder 2005 for example s and se are incorporated into the amino acids cysteine methionine and selenocysteine and selenomethionine respectively whereas the heavy metal te has no known biological function and the 210po can have toxic effects even in small concentrations due to its high energy alpha radiation moroz and parfenov 1972 both s and se are able to exist in a variety of oxidation states thus amino acids containing either of the two elements have powerful redox capabilities moroder 2005 and are often incorporated into enzymes on the other hand the cysteine rich protein metallothionein has the function of an antioxidant and acts as a binding site for heavy metals such as hg cu ag cd pb and zn amiard et al 2006 both s and se are mostly absorbed as sulfate and selenate by s c i e n c e o f t h e t o t a l e n v i r o n m e n t 3 9 2 2 0 0 8 2 1 8 2 2 4 corresponding author tel 82 2 880 7508 fax 82 2 876 6508 e mail address gkim snu ac kr g kim 0048 9697 see front matter 2007 elsevier b v all rights reserved doi 10 1016 j scitotenv 2007 12 003 available at higher plants barceloux 1999 and transferred to consu mers synthesized into organic compounds schlekat et al 2004 lee et al 2006 while s is ubiquitous in every organism in levels of mg g 1dry weight se is an element of which the threshold between essentiality and toxicity can be very narrow and which is also effectively accumu lated along the food chain via trophic transfer lemly 1993 and internally in the hepatopancreas of cephalo pods cappon and smith 1982 liu et al 1987 napole o et al 2005 there has only recently been a focus on the metalloid te in the environmental sciences its abundance level in the earth s crust is very low and although it exhibits a non nutrient behavior in a marine environment lee and edmond 1985 it is assimilated by fungi as well as terrestrial and marine primary producers ramadan et al 1989 nolan et al 1991 chasteen and bentley 2003 although no biological use for te and only moderate bioaccumulation of the element has been found to date markert 1994 has suggested that it may have the potential for an essential function analogous to se despite its toxic properties due to high energy alpha decay the radionuclide 210po is readily assimilated by marine primary producers fisher et al 1983 and further concen trated along the food chain a behavior which has been linked to s uptake cherry and shannon 1974 210po is a member of the natural 238u decay series and it has significant importance as a tracer in environmental studies including processes in the atmosphere kim et al 2000 as well as in the ocean kim 2001 in addition because of its remarkably high activities in marine organisms 210po has been used to characterize the nutritional conditions of pelagic marine habitats heyraud and cherry 1979 and to identify uptake and metabolic pathways in marine inverte brates carvalho and fowler 1994 particularly in visceral organs such as the digestive gland or hepatopancreas of invertebrates and the pyloric caecum of fishes cherry et al 1983 skwarzec 1988a b bustamante et al 2002a very high activities albeit very low concentrations of the radionuclide can be found in contrast to s and se te and 210po probably have no purposeinthelivingorganism neverthelessallfour elements represent a chemically relatively homogeneous group se teand 210po areclassifiedass seeking elements nieboer and richardson 1980 and can follow thesamemetabolicpathways suchasbiomethylation hussainetal 1995 kimetal 2000 chasteenand bentley 2003 in experimental conditions te was readily incorporated into amino acids by fungi in place of se ramadan et al 1989 furthermore se and 210po have similardistributionpatternsdependingontheinternal organsofmarineinvertebratesandfish heyraudand cherry 1979 liu et al 1987 skwarzec 1988a b chatterjee et al 2001 however there is no comprehensive review or study of how the four chalcogens are connected in the higher organism and how their uptake is influenced by the environmental setting therefore we are contributing a complementary dataset on s se te and 210po abundances in muscle stomach gills and hepatopancreas tissues of a squid todarodes pacificus in the east asian marginal seas squid are heavily exploited by commercial fishing a total of 497887 t were caught in 1999 with the largest catches by the korean and japanese fishing fleets consequently a substantial amount of literature is available on the ecology and distribution of this species in the east japan sea yellow sea and northern pacific ocean nesis 1971 okutani 1983 kiyofuji and saitoh 2004 it has characteristic breeding and migration habits kiyofuji and saitoh 2004 and is a bio indicator species for the annual fluctuation of trace metals in its marine habitat since it has an average life span of 1 year is a pelagic top predator with high bioaccumulation potential and comprises a big part of the daily seafood diet of the korean and japanese population yamamoto et al 1994 ichihashi et al 2001 carvalho 1995 estimated that in the portuguese population the primary intake route of 210po for humans is the consumption of seafood such as squids and in a heavy seafood consumer the radionuclide can accumulate to a more than threefold higher activity compared to a person with a terrestrial based diet since korea has a per capita consumption of seafood similar to portugal 50 60 kg per annum there is a need for a closer investigation on the uptake pathways of 210po and its connectivity with chemi cally similar life essential elements such as s and se 2 materials and methods 2 1 sample collection and preparation ten individuals of the species t pacificus were caught at night using trawls and lights 30 miles off the korean east coast towards ulleong island in the east japan sea we assume that based on the migration patterns of the species and the catching location the individuals originated from the autumn spawning population a group which was migrating northeastward from its spawning ground in the east china sea to feeding grounds into the japan east sea along the korean east coast kiyofuji and saitoh 2004 since the squid were caught in late summer they had already reached maturity okutani 1983 after arriving at the laboratory the mantle length body weight and sex of each individual squids were determined then the squid were dissected into stomach mantle muscle hepatopancreas and gill parts and freeze dried at 70 c during the dissection all ingested food were removed from the stomach by squeezing and only the stomach tissue was used for analysis for acid digestion 5 ml of ultra pure hno3and 1 ml of ultra pure h2o2were added to 0 2 g of each dried tissue type in a closed teflon bomb and heated between 180 and 200 c for 4 h after cooling the screw caps of the teflon bombs were removed the solution was evaporated to near dryness and picked up in 10 ml of 0 1 n hno3for analysis of the se and te with icp ms 2 2 chalcogen analysis the samples were measured with a thermo x series icp ms using an id 100 auto dilutor the power setting for the icp ms was 1400 w and three channels were measured in five runs 219s c i e n c e o f t h e t o t a l e n v i r o n m e n t 3 9 2 2 0 0 8 2 1 8 2 2 4 per sample for se and te a scp science standard and an accus science standard were used respectively corrections for instrumental drift and matrix effect were made using an internal rhodium standard scp science detection limits as reagent blank values were 0 06 ppb for te and 0 01 ppb for se the s was measured as sulfate by liquid chromatography using a conductivity waters 432 detector the digested samples in 0 1 n hno3were diluted with diw to 1 20 and analyzed using an ic pak a hc column with a borate gluconate eluent using a standard of special grade anhydrous na2so4dissolved in milli q water a reagent blank value of 0 3 ppm was used as detection limit for 210po analysis an internal209po spike in 0 5 m hno3 was added to the digested sample then the solution was evaporated to dryness to remove the hno3 the evaporate was picked up in weak approximately 0 5 m hcl and ascorbic acid was added until the solution was colorless 210po from the solution was spontaneously deposited onto a silver disc kim et al 1999 mounted on a stirrer and thereafter counted using a canberra alpha analyst with an a450 20 alpha pips detector the reagent blank was about 0 0003 cpm 0 0013 mbq it is important to determine whether the 210po in the samples had been actively accumulated by the organism or whether it resulted from ingrowth of 210pb thus after plating the solution was stored for 6 months to allow ingrowth of 210po from210pb and then the 210po plating step was repeated the210pb of the original sample was determined by correcting the yielded counts for residual 210po from the first plating step and ingrowth time 2 3 statistical analysis descriptives for chalcogen concentrations per tissue type were calculated for correlations between chalcogens pear son tests were applied differences between groups for example for chalcogen concentration differences between male and female squids or for differences between tissues within the squids were determined using the mann whitney u test statistical analysis was conducted using spss 10 0 3 results 3 1 chalcogen concentrations and tissue distribution patterns the se te and 210po all had their highest concentrations in the hepatopancreas and the lowest value in muscle tissue table 1 fig 1 the gills had higher se and 210po concentrations than stomach tissue 210pb values in all tissues were very low compared with 210po on average 3 thus the contribution of 210pb to the210po activities was regarded as negligible in this study for te the stomach concentration was higher than the gill concentration but not significantly s values did not follow the same pattern as the other three chalcogens for the various tissues but were highest in the gills followed by stomach hepatopancreas and muscle tissue nevertheless the muscle tissue still had a significantly lower s concentration than the hepatopancreas tissue mann whitney u test p 0 01 te values overall were very low of the order of ppb compared to the other chalcogens and ranged from 0 9 ng g 1dry weight for muscleandgillsto2 4ngg 1dryweightand3 4ngg 1dryweight for stomach and hepatopancreas respectively no correlations between chalcogen concentrations and mantle length or body weight could be found there were no significant differences between chalcogen concentrations of male and female squids mann whitney u test pn0 05 for all chalcogen concentrations in all four tissue samples for further discussion we therefore pooled the tissue values for male and female squid we applied a pearson correlation for the concentrations of the four elements within the various organs in case of gill and stomach tissues no correlations between the chalcogen elements could be found for the hepatopancreas and muscle tissues s was negatively correlated with all other chalcogens most notably with 210po hepatopancreas r 0 68 p 0 03 mantle r 0 67 p 0 07 table 1 biometric data and tissue chalcogen concentrations per g dry weight of todarodes pacificus nosexmantle length cm body weight g musclestomachgillshepatopancreas s mg se g 210po mbq te ng s mg se g 210po mbq te ng s mg se g 210po mbq te ng s mg se g 210po mbq te ng 1m21 723418 01 7 a0 542 74 7 a12 551 66 41971 046 47 37424 2 2m22 726129 31 6 b1 039 74 524 41 751 17 31090 942 89 56952 4 3f23 029524 51 74 90 637 75 912 40 958 56 22881 021 89 418191 8 4m22 528140 41 54 00 641 74 028 50 762 16 92600 940 07 311382 6 5m22 525136 41 44 60 737 66 420 90 9 a a128 a57 76 010402 7 6f22 726421 81 68 30 5 a a21 5 a43 5 a156 a37 62 612850 5 7m23 329829 81 66 00 636 14 319 60 748 26 42370 929 29 710622 7 8m21 023627 61 46 61 139 7 a20 2 a53 66 41730 733 618 515979 8 9m21 023527 31 85 20 735 83 635 50 753 26 81991 034 910 013562 5 10m23 032820 81 45 72 641 85 970 20 942 47 23350 827 610 413454 8 mean22 326827 61 65 70 939 24 928 12 451 66 72080 937 29 112083 4 sd0 831 76 90 11 30 62 5118 14 16 40 4700 110 34 12692 5 a not measured b no detectable concentration 220s c i e n c e o f t h e t o t a l e n v i r o n m e n t 3 9 2 2 0 0 8 2 1 8 2 2 4 3 2 chalcogens and bioaccumulation bioaccumulation factors were calculated using seawater values and the tissue concentrations of se te and 210po based on a dry weight basis seawater values were taken from suh et al 1995 for dissolved 210po from liu et al 1987 for se and from lee and edmond 1985 for te table 2 shows the bioaccumulation factors for our study based on the reference values as well as for other organisms previously published for se bioaccumulation factors were of the same magnitude in muscle stomach and gill tissue and an order of magnitude higher in the hepatopancreas the te showed overall lower bioaccumulation factors with relatively lower values for gills and muscle and higher values for stomach and hepatopancreas the bioaccumula tion values for 210po in our t pacificus samples reflected the absolute tissue concentrations with an ascending order of musclenstomachngillsnhepatopancreas 4 discussion 4 1 chalcogen concentrations in various tissue types if we convert the s concentrations of the tissues in our study to wet weightsusing the tissue moisture contentknown from other studiesonthesamespecies kimetal 2006 moonetal 2006 we achieve values of 6 3 1 6 mg g 1wet weight and 15 6 4 3 mg g 1 wet weight for the muscle and hepatopancreas respectively which are slightly different from the reported values from t pacificus samples along the japanese coast 4 7 mg g 1wet weight and9 6mgg 1wetweight ichihashietal 2001 butstillshowthe table 2 bioaccumulation factors for 210po se and te based on previously published seawater reference values sample type 210po sete phytoplankton7 6 104 1 6 104 600 4 2 104 zooplankton8 3 105 3 4 104 8 20 loligo sp muscle1 9 104 2 3 104 gills 7 2 104 hepatopancreas2 3 106 1 3 105 todarodes pacificus muscle6 4 1032 0 1045 8 103 stomach2 6 1046 2 1045 9 103 gills2 4 1058 4 1041 6 104 hepatopancreas1 4 1061 1 1052 2 104 sources suh et al 1995 heyraud and cherry 1979 liu et al 1987 nolan et al 1991 data for todarodes pacificus are from this study fig 1 mean chalcogen concentrations in the tissues of todarodes pacificus error bars represent 1 standard deviation mann whitney u tests p 0 05 showed significant differences from other tissue concentrations in muscle and gills for s in muscle and stomach for se in hepatopancreas for te and in muscle stomach gills and hepatopancreas for 210po 221s c i e n c e o f t h e t o t a l e n v i r o n m e n t 3 9 2 2 0 0 8 2 1 8 2 2 4 same distribution pattern with relatively higher values in the hepatopancreas than in muscle tissue and overall substantially higher concentrations than the other chalcogens the distribution patterns of se te and 210po concentrations in the squid organs are similar to those of trace and heavy metals smith et al 1984 with extraordinarily high concentra tions in the hepatopancreas and very low concentrations in the muscletissues asmentionedinsection3 1 wewereabletofind slightdifferencesbetweenthese teand210poconcentrationsof male and female squids albeit these differences were not statistically significant since our samples consisted of eight male and only two female specimens we cannot draw valid conclusionsfromtheseresults itisplausiblethat solongasthe foodsourceisth