Steepest ascent tariff reform

The policy reform literature is primarily concerned with the construction of reforms that yield welfare gains. By contrast, this paper’s contribution is to develop a theoretical concept for which the focus is upon the sizes of welfare gains accruing from policy reforms rather than upon their signs. In undertaking this task, and by focusing on tariff reforms, we introduce the concept of a steepest ascent policy reform, which is a locally optimal reform in the sense that it achieves the highest marginal gain in utility of any feasible local reform. We argue that this reform presents itself as a natural benchmark for the evaluation of the welfare effectiveness of other popular tariff reforms such as the proportional tariff reduction and the concertina rules, since it provides the maximal welfare gain of all possible local reforms. We derive properties of the steepest ascent tariff reform, construct an index to measure the relative welfare effectiveness of any given tariff reform, determine conditions under which proportional and concertina reforms are locally optimal and provide illustrative examples.

Tariff strategies and small open economies

In this paper we examine the issue of optimal tariffs for a small economy that trades with a large economy. We define ‘small’ and ‘large’ in the sense that the world prices are determined solely by the large country, and, therefore, the small country faces exogenously given world prices. Within this framework it is shown that there exist situations in which the small country has an incentive to behave as a Stackelberg leader by committing itself to a non-zero optimal tariff. Although the small country is unable to directly affect world prices, by pre-committing to a non-zero trade tax it may induce a reduction of the large country's optimal trade tax, thereby indirectly improving its terms of trade and welfare. JEL Classification: F13, F35

Tariff-tax reforms and market access

Reducing tariffs and increasing consumption taxes is a standard IMF advice to countries that want to open up their economy without hurting government finances. Indeed, theoretical analysis of such a tariff–tax reform shows an unambiguous increase in welfare and government revenues. The present paper examines whether the country that implements such a reform ends up opening up its markets to international trade, i.e. whether its market access improves. It is shown that this is not necessarily so. We also show that, comparing to the reform of only tariffs, the tariff–tax reform is a less efficient proposal to follow both as far as it concerns market access and welfare.

Taxes and decision rights in multinationals

We examine how a multinational's choice to centralize or decentralize its decision structure is affected by country tax differentials. Within a simple model that emphasizes the multiple conflicting roles of transfer prices in multinational enterprises (MNEs)—here, as a strategic precommitment device and a tax manipulation instrument—we show that centralization is more profitable when tax differentials are large. When tax differentials are small, decentralization can be performed in two different ways each providing the highest profits in a particular range of the tax differential. Hence, the paper emphasizes the organizational flexibility that MNEs have in pursuing tax optimization.

Tied aid, unemployment and welfare

The effect of foreign aid on the welfare levels of both the recipient and the donor country has been a much analysed topic for research in both the theory of international trade and development economics. In the development economics literature, concerns have been raised since the 1960s on the possible adverse effect of foreign aid on domestic savings and growth.1 The trade theory literature in this respect is much older and dates back to the 1920s when Professors Keynes and Ohlin debated on the effect of foreign aid on international terms of trade.2 Ever since, the terms of trade effect has been the cornerstone in the analysis of the welfare effect of foreign aid in the trade theory literature.3 After some early confusion, it is now well established that in a Walrasian stable world economy with two countries, a necessary condition for foreign aid to have perverse effects is that there is some distortion in either of the two countries.4 It is also known that, under normality and substitutability of goods, untied aid cannot be strictly Pareto-improving in a tariff distorted world.5

Transfer pricing rules and competing governments

The literature on the regulation of multinationals' transfer prices has not considered the possibility that governments may use transfer pricing rules strategically when they compete with other governments. The present paper analyses this case and shows that, even in the absence of agency considerations, a non‐cooperative equilibrium is characterised by above‐optimal levels of effective taxation. We then derive conditions under which harmonization of transfer pricing rules lead to a Pareto improvement, and show that harmonization according to the ‘arm's length’ principle—the form of harmonization advocated by the OECD—may not be Pareto improving.

Effects of turbidity on feeding and distribution of fish

In aquatic systems, the ability of both the predator and prey to detect each other may be impaired by turbidity. This could lead to significant changes in the trophic interactions in the food web of lakes. Most fish use their vision for predation and the location of prey can be highly influenced by light level and clarity of the water environment. Turbidity is an optical property of water that causes light to be scattered and absorbed by particles and molecules. Turbidity is highly variable in lakes, due to seasonal changes in suspended sediments, algal blooms and wind-driven suspension of sediments especially in shallow waters. There is evidence that human activity has increased erosion leading to increased turbidity in aquatic systems. Turbidity could also play a significant role in distribution of fish. Turbidity could act as a cover for small fish and reduce predation risk. Diel horizontal migration by fish is common in shallow lakes and is considered as consequences of either optimal foraging behaviour for food or as a trade-off between foraging and predator avoidance. In turbid lakes, diel horizontal migration patterns could differ since turbidity can act as a refuge itself and affect the predator-prey interactions. Laboratory experiments were conducted with perch (Perca fluviatilis L.) and white bream (Abramis björkna (L.)) to clarify the effects of turbidity on their feeding. Additionally to clarify the effects of turbidity on predator preying on different types of prey, pikeperch larvae (Sander lucioperca (L.)), Daphnia pulex (Leydig), Sida crystallina (O.F. Müller), and Chaoborus flavicans (Meigen) were used as prey in different experiments. To clarify the role of turbidity in distribution and diel horizontal migration of perch, roach (Rutilus rutilus (L.)) and white bream, field studies were conducted in shallow turbid lakes. A clear and a turbid shallow lake were compared to investigate distribution of perch and roach in these two lakes in a 15-year study period. Feeding efficiency of perch and white bream was not significantly affected with increasing clay turbidity up to 50 NTU. The perch experiments with pikeperch larvae suggested that clay turbidity could act as a refuge especially at turbidity levels higher than 50 NTU. Perch experiments with different prey types suggested that pikeperch larvae probably use turbidity as a refuge better compared to Daphnia. Increase in turbidity probably has stronger affect on perch predating on plant-attached prey. The main findings of the thesis show that turbidity can play a significant role in distribution of fish. Perch and roach could use turbidity as refuge when macrophytes disappear while small perch may also use high turbidity as refuge when macrophytes are present. Floating-leaved macrophytes are probably good refuges for small fish in clay-turbid lakes and provide a certain level of turbidity and not too complex structure for refuge. The results give light to the predator-prey interactions in turbid environments. Turbidity of water should be taken in to account when studying the diel horizontal migrations and distribution of fish in shallow lakes.

Disarming identities : Ethnic identities in conflict resolution: Hindrance or helpful resource?

This thesis proposes that national or ethnic identity is an important and overlooked resource in conflict resolution. Usually ethnic identity is seen both in international relations and in social psychology as something that fuels the conflict. Using grounded theory to analyze data from interactive problem-solving workshops between Palestinians and Israelis a theory about the role of national identity in turning conflict into protracted conflict is developed. Drawing upon research from, among others, social identity theory, just world theory and prejudice it is argued that national identity is a prime candidate to provide the justification of a conflict party’s goals and the dehumanization of the other necessary to make a conflict protracted. It is not the nature of national identity itself that lets it perform this role but rather the ability to mobilize a constituency for social action (see Stürmer, Simon, Loewy, & Jörger, 2003). Reicher & Hopkins (1996) have demonstrated that national identity is constructed by political entrepreneurs to further their cause, even if this construction is not a conscious one. Data from interactive problem-solving workshops suggest that the possibility of conflict resolution is actually seen by participants as a direct threat of annihilation. Understanding the investment necessary to make conflict protracted this reaction seems plausible. The justification for ones actions provided by national identity makes the conflict an integral part of a conflict party’s identity. Conflict resolution, it is argued, is therefore a threat to the very core of the current national identity. This may explain why so many peace agreements have failed to provide the hoped for resolution of conflict. But if national identity is being used in a constructionist way to attain political goals, a political project of conflict resolution, if it is conscious of the constructionist process, needs to develop a national identity that is independent of conflict and therefore able to accommodate conflict resolution. From this understanding it becomes clear why national identity needs to change, i.e. be disarmed, if conflict resolution is to be successful. This process of disarmament is theorized to be similar to the process of creating and sustaining protracted conflict. What shape and function this change should have is explored from the understanding of the role of national identity in supporting conflict. Ideas how track-two diplomacy efforts, such as the interactive problem-solving workshop, could integrate a process by both conflict parties to disarm their respective identities are developed.

Lasten ja nuorten kokemuksia lastensuojelun alkuvaiheen arvioinnista

Tämän tutkielman tarkoituksena on kuvailla lasten ja nuorten kokemuksia heidän osallistuttuaan perheineen lastensuojelun alkuvaiheen arviointiin eli lastensuojelutarpeen selvitykseen. Tarkastelen tutkielmassa lasten ja nuorten kokemuksia osallisuuden näkökulmasta. Tavoitteena on, että tämä tutkielma kertoisi lastensuojelutarpeen selvityksestä työkäytäntönä ja lisäisi tietoa siitä, miten lastensuojelu on onnistunut tavoitteessaan lisätä lasten ja nuorten osallisuuden kokemuksia ja lapsilähtöisyyttä lastensuojelun työkäytäntöihin ja erityisesti asiakkuuden alkuvaiheen selvitystyöhön. Tutkielmani on laadullinen tutkimus, jonka aineisto on saatu haastattelemalla yhdeksää 10–17-vuotiasta lasta ja nuorta, jotka ovat osallistuneet lastensuojelutarpeen selvitykseen vuosien 2009–2010 aikana. Lastensuojeluasiakkuus oli päättynyt arvioinnin jälkeen neljän nuoren osalta ja viiden nuoren kohdalla oli päädytty jatkamaan asiakkuutta lastensuojelun avohuollossa. Tutkimusaineiston analysoinnissa käytin temaattista sisällönanalyysiä. Thomasin malli osallisuuden ulottuvuuksista auttoi jäsentämään osallisuuden käsitettä ja lasten ja nuorten puhetta. Tutkimusaineistossa osallisuuden kokemuksen osa-alueiksi muodostuivat 1) tiedon saaminen asiakkuuden alkuvaiheesta ja syistä, jotka johtivat lastensuojelutarpeen selvitykseen, 2) kuulluksi tuleminen ja 3) vaikuttamisen mahdollisuus selvitystyön aikana. Useimmat lapset ja nuoret antoivat kiitettävän arvosanan tiedon saannistaan. Kuulluksi tuleminen edellytti mahdollisuutta itsensä ilmaisemiseen ja tuen saamista siihen. Lastensuojeluun kehitetyt osallistavat menetelmät olivat auttaneet oman mielipiteen kertomisessa. Vaikuttamisen mahdollisuus tarkentui mahdollisuudeksi vaikuttaa siihen, ketkä osallistuivat selvitykseen sekä mahdollisuudeksi vaikuttaa selvityksen sisältöön. Vaikuttamisen mahdollisuuteen sisältyi lisäksi mahdollisuus olla osallistumatta. Osallisuuden kokemukseen vaikuttivat myös se, näkyikö nuoren oma mielipide yhteenvetotekstissä ja se, oliko nuori selvillä asiakassuunnitelman tavoitteista. Kuulluksi tuleminen oli vaikuttanut nuorten käsityksiin lastensuojelusta ja muuttanut niitä positiivisemmiksi. Kuulluksi tulemisen ja osallisuuden kokemuksen seurauksena nuoret kokivat pääsääntöisesti hyötyneensä alkuvaiheen interventiosta. Eniten nuoret mainitsivat emotionaalisesti merkittäviä muutoksia, kuten luottamuksen ja yhteisen keskustelun lisääntymisen perheenjäsenten välillä ja hyväksytyksi tulemisen kokemuksia. Selvitykseen osallistumisen koettiin vaikuttaneen sekä lasten ja nuorten omaan käyttäytymiseen että vanhempien asennoitumiseen positiivisella tavalla. Tärkeimmät lähteet: Muukkonen, Tiina & Tulensalo, Hanna (2004): Kohtaavaa lastensuojelua. Möller (2005): Arviosta sanoisin – Tutkimus lastensuojelun asiakkuuden alkuvaiheeseen liittyvän arvioinnin mallintamisesta. Oranen, Mikko (2008): Mitä mieltä? Mitä mieltä? Lasten osallisuus lastensuojelun kehittämisessä.

Magnetically induced currents and magnetic response properties of molecules

The magnetically induced currents in organic monoring and multiring molecules, in Möbius shaped molecules and in inorganic all-metal molecules have been investigated by means of the Gauge-including magnetically induced currents (GIMIC) method. With the GIMIC method, the ring-current strengths and the ring-current density distributions can be calculated. For open-shell molecules, also the spin current can be obtained. The ring-current pathways and ring-current strengths can be used to understand the magnetic resonance properties of the molecules, to indirectly identify the effect of non-bonded interactions on NMR chemical shifts, to design new molecules with tailored properties and to discuss molecular aromaticity. In the thesis, the magnetic criterion for aromaticity has been adopted. According to this, a molecule which has a net diatropic ring current might be aromatic. Similarly, a molecule which has a net paratropic current might be antiaromatic. If the net current is zero, the molecule is nonaromatic. The electronic structure of the investigated molecules has been resolved by quantum chemical methods. The magnetically induced currents have been calculated with the GIMIC method at the density-functional theory (DFT) level, as well as at the self-consistent field Hartree-Fock (SCF-HF), at the Møller-Plesset perturbation theory of the second order (MP2) and at the coupled-cluster singles and doubles (CCSD) levels of theory. For closed-shell molecules, accurate ring-current strengths can be obtained with a reasonable computational cost at the DFT level and with rather small basis sets. For open-shell molecules, it is shown that correlated methods such as MP2 and CCSD might be needed to obtain reliable charge and spin currents. The basis set convergence has to be checked for open-shell molecules by performing calculations with large enough basis sets. The results discussed in the thesis have been published in eight papers. In addition, some previously unpublished results on the ring currents in the endohedral fullerene Sc3C2@C80 and in coronene are presented. It is shown that dynamical effects should be taken into account when modelling magnetic resonance parameters of endohedral metallofullerenes such as Sc3C2@C80. The ring-current strengths in a series of nano-sized hydrocarbon rings are related to static polarizabilities and to H-1 nuclear magnetic resonance (NMR) shieldings. In a case study on the possible aromaticity of a Möbius-shaped [16]annulene we found that, according to the magnetic criterion, the molecule is nonaromatic. The applicability of the GIMIC method to assign the aromatic character of molecules was confirmed in a study on the ring currents in simple monocylic aromatic, homoaromatic, antiaromatic, and nonaromatic hydrocarbons. Case studies on nanorings, hexaphyrins and [n]cycloparaphenylenes show that explicit calculations are needed to unravel the ring-current delocalization pathways in complex multiring molecules. The open-shell implementation of GIMIC was applied in studies on the charge currents and the spin currents in single-ring and bi-ring molecules with open shells. The aromaticity predictions that are made based on the GIMIC results are compared to other aromaticity criteria such as H-1 NMR shieldings and shifts, electric polarizabilities, bond-length alternation, as well as to predictions provided by the traditional Hückel (4n+2) rule and its more recent extensions that account for Möbius twisted molecules and for molecules with open shells.

Lasten ja nuorten kokemuksia lastensuojelun alkuvaiheen arvioinnista

Tämän tutkielman tarkoituksena on kuvailla lasten ja nuorten kokemuksia heidän osallistuttuaan perheineen lastensuojelun alkuvaiheen arviointiin eli lastensuojelutarpeen selvitykseen. Tarkastelen tutkielmassa lasten ja nuorten kokemuksia osallisuuden näkökulmasta. Tavoitteena on, että tämä tutkielma kertoisi lastensuojelutarpeen selvityksestä työkäytäntönä ja lisäisi tietoa siitä, miten lastensuojelu on onnistunut tavoitteessaan lisätä lasten ja nuorten osallisuuden kokemuksia ja lapsilähtöisyyttä lastensuojelun työkäytäntöihin ja erityisesti asiakkuuden alkuvaiheen selvitystyöhön. Tutkielmani on laadullinen tutkimus, jonka aineisto on saatu haastattelemalla yhdeksää 10–17-vuotiasta lasta ja nuorta, jotka ovat osallistuneet lastensuojelutarpeen selvitykseen vuosien 2009–2010 aikana. Lastensuojeluasiakkuus oli päättynyt arvioinnin jälkeen neljän nuoren osalta ja viiden nuoren kohdalla oli päädytty jatkamaan asiakkuutta lastensuojelun avohuollossa. Tutkimusaineiston analysoinnissa käytin temaattista sisällönanalyysiä. Thomasin malli osallisuuden ulottuvuuksista auttoi jäsentämään osallisuuden käsitettä ja lasten ja nuorten puhetta. Tutkimusaineistossa osallisuuden kokemuksen osa-alueiksi muodostuivat 1) tiedon saaminen asiakkuuden alkuvaiheesta ja syistä, jotka johtivat lastensuojelutarpeen selvitykseen, 2) kuulluksi tuleminen ja 3) vaikuttamisen mahdollisuus selvitystyön aikana. Useimmat lapset ja nuoret antoivat kiitettävän arvosanan tiedon saannistaan. Kuulluksi tuleminen edellytti mahdollisuutta itsensä ilmaisemiseen ja tuen saamista siihen. Lastensuojeluun kehitetyt osallistavat menetelmät olivat auttaneet oman mielipiteen kertomisessa. Vaikuttamisen mahdollisuus tarkentui mahdollisuudeksi vaikuttaa siihen, ketkä osallistuivat selvitykseen sekä mahdollisuudeksi vaikuttaa selvityksen sisältöön. Vaikuttamisen mahdollisuuteen sisältyi lisäksi mahdollisuus olla osallistumatta. Osallisuuden kokemukseen vaikuttivat myös se, näkyikö nuoren oma mielipide yhteenvetotekstissä ja se, oliko nuori selvillä asiakassuunnitelman tavoitteista. Kuulluksi tuleminen oli vaikuttanut nuorten käsityksiin lastensuojelusta ja muuttanut niitä positiivisemmiksi. Kuulluksi tulemisen ja osallisuuden kokemuksen seurauksena nuoret kokivat pääsääntöisesti hyötyneensä alkuvaiheen interventiosta. Eniten nuoret mainitsivat emotionaalisesti merkittäviä muutoksia, kuten luottamuksen ja yhteisen keskustelun lisääntymisen perheenjäsenten välillä ja hyväksytyksi tulemisen kokemuksia. Selvitykseen osallistumisen koettiin vaikuttaneen sekä lasten ja nuorten omaan käyttäytymiseen että vanhempien asennoitumiseen positiivisella tavalla. Tärkeimmät lähteet: Muukkonen, Tiina & Tulensalo, Hanna (2004): Kohtaavaa lastensuojelua. Möller (2005): Arviosta sanoisin – Tutkimus lastensuojelun asiakkuuden alkuvaiheeseen liittyvän arvioinnin mallintamisesta. Oranen, Mikko (2008): Mitä mieltä? Mitä mieltä? Lasten osallisuus lastensuojelun kehittämisessä.

Molecular Characterization of Viruses Causing the Cassava Brown Streak Disease Epidemic in Eastern Africa

Cassava brown streak disease (CBSD) was described for the first time in Tanganyika (now Tanzania) about seven decades ago. Tanganyika (now Tanzania) about seven decades ago. It was endemic in the lowland areas of East Africa and inland parts of Malawi and caused by Cassava brown streak virus (CBSV; genus Ipomovirus; Potyviridae). However, in 1990s CBSD was observed at high altitude areas in Uganda. The causes for spread to new locations were not known.The present work was thus initiated to generate information on genetic variability, clarify the taxonomy of the virus or viruses associated with CBSD in Eastern Africa as well as to understand the evolutionary forces acting on their genes. It also sought to develop a molecular based diagnostic tool for detection of CBSD-associated virus isolates. Comparison of the CP-encoding sequences of CBSD-associated virus isolates collected from Uganda and north-western Tanzania in 2007 and the partial sequences available in Genbank revealed occurrence of two genetically distinct groups of isolates. Two isolates were selected to represent the two groups. The complete genomes of isolates MLB3 (TZ:Mlb3:07) and Kor6 (TZ:Kor6:08) obtained from North-Western (Kagera) and North-Eastern (Tanga) Tanzania, respectively, were sequenced. The genomes were 9069 and 8995 nucleotides (nt), respectively. They translated into polyproteins that were predicted to yield ten mature proteins after cleavage. Nine proteins were typical in the family Potyviridae, namely P1, P3, 6K1, CI, 6K2, VPg, NIa-Pro, NIb and CP, but the viruses did not contain HC-Pro. Interestingly, genomes of both isolates contained a Maf/HAM1-like sequence (HAM1h; 678 nucleotides, 25 kDa) recombined between the NIb and CP domains in the 3’-proximal part of the genomes. HAM1h was also identified in Euphorbia ringspot virus (EuRSV) whose sequence was in GenBank. The HAM1 gene is widely spread in both prokaryotes and eukaryotes. In yeast (Saccharomyces cerevisiae) it is known to be a nucleoside triphosphate (NTP) pyrophosphatase. Novel information was obtained on the structural variation at the N-termini of polyproteins of viruses in the genus Ipomovirus. Cucumber vein yellowing virus (CVYV) and Squash vein yellowing virus (SqVYV) contain a duplicated P1 (P1a and P1b) but lack the HC-Pro. On the other hand, Sweet potato mild mottle virus (SPMMV), has a single but large P1 and has HC-Pro. Both virus isolates (TZ:Mlb3:07 & TZ:Kor6:08) characterized in this study contained a single P1 and lacked the HC-Pro which indicates unique evolution in the family Potyviridae. Comparison of 12 complete genomes of CBSD-associated viruses which included two genomes characterized in this study, revealed genetic identity of 69.0–70.3% (nt) and amino acid (aa) identities of 73.6–74.4% at polyprotein level. Comparison was also made among 68 complete CP sequences, which indicated 69.0-70.3 and 73.6-74.4 % identity at nt and aa levels, respectively. The genetic variation was large enough for dermacation of CBSD-associated virus isolates into two distinct species. The name CBSV was retained for isolates that were related to CBSV isolates available in database whereas the new virus described for the first time in this study was named Ugandan cassava brown streak virus (UCBSV) by the International Committee on Virus Taxonomy (ICTV). The isolates TZ:Mlb3:07 and TZ:Kor6:08 belong to UCBSV and CBSV, respectively. The isolates of CBSV and UCBSV were 79.3-95.5% and 86.3-99.3 % identitical at nt level, respectively, suggesting more variation amongst CBSV isolates. The main sources of variation in plant viruses are mutations and recombination. Signals for recombination events were detected in 50% of isolates of each virus. Recombination events were detected in coding and non-coding (3’-UTR) sequences except in the 5’UTR and P3. There was no evidence for recombination between isolates of CBSV and UCBSV. The non-synonomous (dN) to synonomous (dS) nucleotide substitution ratio (ω) for the HAM1h and CP domains of both viruses were ≤ 0.184 suggesting that most sites of these proteins were evolving under strong purifying selection. However, there were individual amino acid sites that were submitted to adaptive evolution. For instance, adaptive evolution was detected in the HAM1h of UCBSV (n=15) where 12 aa sites were under positive selection (P< 0.05) but not in CBSV (n=12). The CP of CBSV (n=23) contained 12 aa sites (p<0.01) while only 5 aa sites in the CP gene of UCBSV were predicted to be submitted to positive selection pressure (p<0.01). The advantages offered by the aa sites under positive selection could not be established but occurrence of such sites in the terminal ends of UCBSV-HAMIh, for example, was interpreted as a requirement for proteolysis during polyprotein processing. Two different primer pairs that simultaneously detect UCBSV and CBSV isolates were developed in this study. They were used successfully to study distribution of CBSV, UCBSV and their mixed infections in Tanzania and Uganda. It was established that the two viruses co-infect cassava and that incidences of co-infection could be as high as 50% around Lake Victoria on the Tanzanian side. Furthermore, it was revealed for the first time that both UCBSV and CBSV were widely distributed in Eastern Africa. The primer pair was also used to confirm infection in a close relative of cassava, Manihot glaziovii (Müller Arg.) with CBSV. DNA barcoding of M. glaziovii was done by sequencing the matK gene. Two out of seven M. glaziovii from the coastal areas of Korogwe and Kibaha in north eastern Tanzania were shown to be infected by CBSV but not UCBSV isolates. Detection in M. glaziovii has an implication in control and management of CBSD as it is likely to serve as virus reservoir. This study has contributed to the understanding of evolution of CBSV and UCBSV, which cause CBSD epidemic in Eastern Africa. The detection tools developed in this work will be useful in plant breeding, verification of the phytosanitary status of materials in regional and international movement of germplasm, and in all diagnostic activities related to management of CBSD. Whereas there are still many issues to be resolved such as the function and biological significance of HAM1h and its origin, this work has laid a foundation upon which the studies on these aspects can be based.

Toxicity and imaging of multi-walled carbon nanotubes in human macrophage cells.

Multi-walled carbon nanotubes (MWNTs) have been proposed for use in many applications and concerns about their potential effect on human health have led to the interest in understanding the interactions between MWNTs and human cells. One important technique is the visualisation of the intracellular distribution of MWNTs. We exposed human macrophage cells to unpurified MWNTs and found that a decrease in cell viability was correlated with uptake of MWNTs due to mainly necrosis. Cells treated with purified MWNTs and the main contaminant Fe(2)O(3) itself yielded toxicity only from the nanotubes and not from the Fe(2)O(3). We used 3-D dark-field scanning transmission electron microscopy (DF-STEM) tomography of freeze-dried whole cells as well as confocal and scanning electron microscopy (SEM) to image the cellular uptake and distribution of unpurified MWNTs. We observed that unpurified MWNTs entered the cell both actively and passively frequently inserting through the plasma membrane into the cytoplasm and the nucleus. These suggest that MWNTs may cause incomplete phagocytosis or mechanically pierce through the plasma membrane and result in oxidative stress and cell death.