1. The former Special Rapporteur of the UN International Law Commission on the topic of ‘Non-navigational uses of international watercourses’, Schwebel, S., used ‘significant’ and ‘substantial’ in the sense of ‘serious’. Cf., ILC Yearbook 1982 Vol. II Part 1 p. 100Google Scholar. For the present Special Rapporteur, S. McCaffrey:‘… “appreciable” harm is harm that is significant – i.e., not trivial or inconsequential – but less than “substantial”’: Fourth Report, 1988, A/CN.4/412/Add.2, p. 6. Yet another definition is given by the Experts Group on International Environmental Law of the ‘World Commission on Environment and Development’ (WCED): ‘The duty not to cause substantial – in the sense of significant or not minor – harm…’ See their Environmental Protection and Sustainable Development. Legal Principles and Recommendations (1987) p. 77. As distinct from this approach, according to the Special Rapporteur of the International Law Commission on the topic of ‘international liability for injurious consequences arising out of acts not prohibited by international law’: ‘The word “appreciable” seems to denote an appropriate threshold of tolerance… the words “significant”, “important”, or “substantial” … give an idea of higher thresholds’: Fifth Report, 1989, A/CN.4/423, p. 14, para. 25.

2. Thus, e.g., it seems that within the International Law Commission the long-standing dispute on the use of the term ‘appreciable’ is partly due to differences in the use of this term between the ‘Liability’ and ‘Watercourses’ codification projects. See infra, nn. 35 and 36.

3. UNRIAA, Vol. III, p. 1965Google Scholar.

4. A similar standard was applied by the US Supreme Court in comparable disputes between federal States. E.g., in the dispute between Georgia and Tennessee the Court decided that trans-boundary air pollution by SO₂ emissions should not be tolerated if they reached ‘a great scale”. Cf., 206 US 230 (1907), 27 S Ct 618, 619. In two further cases it stated that: ‘… this court should only intervene to enjoin the action of one State at the instance of another when the case is of serious magnitude, clearly and fully proved…’ See Missouri v. Illinois, 200 US 496(1906) and New York v. New Jersey, 256 US 2% (1921).

5. In most cases international tribunals regarded serious transboundary harm as a breach of obligations under international law: e.g., the German Supreme Court (Staatsgerichtshof) in the Donauversinkungsfallcase held that: ‘Every State is subject to limitations based on general principles of international law precluding it from infringing the rights of another member of the international community. No State has the right to cause substantial injury to the interests of another State by the use it makes of the waters of a natural waterway’. RGZ Vol. 116, Anh. p. 37. English text in Annual Digest of Public International Law Cases(1927–28) p. 128. The tribunal in the TYail Smeltercase held that: ‘… the Dominion of Canada is responsible in international law for the conduct of the Trail Smelter… it is, therefore, the duty of the Government… to see to it that this conduct should be in conformity with the obligation of the Dominion under international law as herein determined.’ UNRIAA, Vol. Ill, p. 1965 et seq. and p. 1963. Cf., also the decision of the PCIJ in the Diversion of waterfront the Meuse case, June 26, 1936: PCIJ, Series A/B No. 70, p. 4 et seq.

6. Threshold qualifications such as ‘serious’ or ‘important’ dominated the language of relevant resolutions of international organisations and expert bodies in that period. The Institut de Droit International defined in a resolution on the utilization of international watercourses as unacceptable ‘serious interference’ and ‘serious modifications’ of such watercourses. Cf., 24 Annuaire (1911) p. 365 et seq., especially paras. I and 11(2). For further sources from this period see, inter alia, S.Schwebel, Third Report, ILC Yearbook 1982 Vol. II Part. 1, p. 91 et seq.

7. This is particularly true for the preventive aspect of the arbitral award which not only established a total amount of compensation of US$ 378,000 but also set up a regime for the operation of the smelter designed to prevent the occurrence of further harm. Cf., UNRIAA, Vol. III, p. 1966.

8. Cf., Sand, P. and Contini, P., ‘Methods to Expedite Environmental Protection: International Ecostandards’, 66 AJIL (1972) p.37Google Scholar.

9. See, eg., Art. 3 of the 1980 Memorandum of Intent between the USA and Canada on transboundary air pollution (‘significant risk of… pollution’), text in Rüster, B., Simma, B., Bock, M., International Protection of the Environment (1982) Vol. XXVIII, p. 352Google Scholar; cf., Art. 2 of the Agreement on boundary rivers between Bulgaria and Turkey (‘substantial damage’) in UNTS, Vol. 807 p. 124; Art. 3 of the Agreement between Finland and Sweden on boundary watercourses (‘substantial deterioration’, ‘significant nature conservancy loss’); cf., UNTS, Vol. 825 p. 272; Art. 58 of the 1960 Agreement between the Federal Republic of Germany and the Netherlands (‘substantial prejudice to the neighbouring State’); cf., ibid., Vol. 508 p. 190. See also Annex III (on transboundary shipments of hazardous wastes and hazardous substances) to the Agreement between the USA and Mexico on the protection of the environment in the border area (‘significant impact on the environment’) in 22 ILM (1983) p. 1025.

10. See, e.g., Art. 5 of the 1979 Convention on Long-Range Transboundary Air Pollution, text in ILM (1979); Art. 1 para. 2 of the 1985 Vienna Convention on the Protection of the Ozone Layer (‘significant deleterious effects’), text in 26 ILM (1987) p. 1529; see also Art. 206 of the 1982 UN Law of the Sea Convention (‘substantial pollution’, ‘significant and harmful changes’); cf., Annex 5, Regulation 1 to the 1974 Helsinki Convention on the Protection of the Baltic Sea, text in UN Doc. ST/LEG/SER.B/18, pp. 518–547; Art. 16 of the 1986 Noumea Convention (‘substantial pollution’ and ‘significant and harmful changes’), as well as similar provisions in other regional seas conventions prepared under the auspices of the UNEP, texts in: Sand, P., Marine Environment Law in the United Nations Environment Programme. An Emergent Eco-Regime (1988);Google Scholar Art. 4 and Art. 5 of the River Senegal and the Lake Chad Conventions (‘modification sensible’, and ‘influence sensible’, respectively), cited in Schwebel, S., Third Report, ILC Yearbook 1982 Vol. II Part 1 p. 99Google Scholar.

11. Art. X of the ILA ‘Helsinki Rules’ (‘substantial injury’) See: ILA, Report of the 52. Conf.1966(1967) pp. 484–532; cf., also Art. 3 of the ILA Montreal Rules applicable to transboundary pollution and Art. 1 of the ILA Montreal Rules on the pollution of international rivers: ILA, Report of the Sixtieth Conference(1982) p. 1 et seq. and p. 13 et seq. (‘substantial injury’); see also Art. 9 (‘substantial harm’) of the Cairo Resolution of the Institut de Droit Internationalon Transboundary Air Pollution, Cairo 13–22 September 1987; see also paras. 5 and 6 of the ‘American Declaration on the Environment adopted at the 1989 Session of the Inter-American Juridical Committee in Rio de Janeiro, CJI/Res.II–2/89.

12. See, e.g., para. 1 of the UNEP Goals and Principles of Environmental Impact Assessment (‘significantly affect the environment’) in UNEP Environmental Law, Guidelines and Principles No. 9 (1987) p. 1Google Scholar; and also Principle ‘E’ of the OECD Principles Concerning Transfrontier Pollution (‘significant risk of transfrontier pollution’) in OECD (1979) pp. 106–112; see also Art. 2.1 (‘significant adverse transboundary environmental impact’) in the ECE Draft Convention on Environmental Impact Assessment in a Transboundary Context, ECE ENVWA/AC.3/R.5, 13 March 1990, p. 6.

13. For further studies on State practice confirming the dominance of such attributes as ‘substantial’, ‘significant’, ‘sensible1’(French), ‘erheblich’(German), cf., the Survey of State Practice Relevant to International Liability for Injurious Consequences Arising out of Acts not Prohibited by International Law, prepared by the UN-Secretariat: A/CN.4/384, 16 October 1984, pp. 67–106. Cf., also the sources cited in Schwebel's, S. Third Report, ILC Yearbook 1982 Vol. II, Part 1 pp. 96–100Google Scholar, and Handl, G., ‘Balancing of Interests and International Liability for the Pollution of International Watercourses: Customary Principles of Law Revisited’, 13 Canadian YIL (1975) pp. 156–174Google Scholar.

14. As defined, eg., in the 1977 Protocol I Additional to the Geneva Conventions of 1949 and the Convention on the prohibition of military and other hostile environmental modification techniques of 1977. Instances of such severe environmental damage may give rise to a regime of responsibility for international crimes. Cf., Art. 19 para. 3(d) of the ILC Draft on State Responsibility and the commentary thereto in ILC Yearbook 1976 Vol. II Part 2 pp. 95–122.

15. This seems to be the case, e.g., in the Law of the Sea Convention where according to Art.19 para. 2(h) ‘wilful and serious’ pollution of the territorial sea by foreign ships is considered contrary to the regime of innocent passage and may entail the enforcement measures by the coastal State provided for in Art. 25. As distinct from this regime, the obligations of States concerning the protection of the marine environment in Part XII of the LOS Convention are either limited to ‘substantial discharge and significant pollution’ (Art. 220(5)) or do not contain any qualifying criteria. On a possible distinction between ‘significant’ and ‘serious’ transboundary environmental harm, cf., also S. McCaffrey, Fourth Report, A/CN.4/412/Add.2, p. 13 para. 11 and p. 14 para.13. A certain differentiation may also be seen in the separate treatment of the so-called substances which are ‘toxic, persistent and liable to bioaccumulate’. Cf., the decision of the Second North Sea Conference to reduce until 1995 the input of such substances by 50%. Cf., the text of the ‘Ministerial Declaration’ in International Journal of Estuarine and Coastal Law (1988) no. 3, p. 254.Google Scholar

16. The 1978 UNEP Guidelines on Shared Natural Resources define ‘significant effects’ as ‘any appreciable effects on a shared natural resource and excludes de minimiseffects’, UNEP Draft Principles of Conduct on Shared Natural Resources, UNEP/1G.12/2, Annex to UNEP/GC.6/17. According to the 1952 ECE study on ‘Legal aspects of hydroelectric development of rivers and lakes’ (published as UN Doc. E/ECE/136E/ECE/EP/ 98/Rev.l.) ‘slight or minor injury’ is to be tolerated. See also Art. 10 of the WCED Legal Principles and Recommendations which reads: ‘States shall… prevent or abate any transboundary environmental interference or a significant risk thereof which causes substantial harm – i.e., harm which is not minor or insignificant’ The commentary to Art. 10 explains that this obligation ‘does not involve a duty to prevent or abate every transboundary harm, however small’, cf., supra n. 1, pp. 76–78.

Most definitions are ‘negative’. E.g., for S. McCaffrey, appreciable harm is ‘not trivial or inconsequential’, cf., Fourth Report, 1988, A/CN.4/412/Add.2, p. 7. A similar definition was given by S. Schwebel – ‘More in quantity than perceptible or only barely detectable”, Third Report, ILC Yearbook 1982 Part 11(1) p. 100.

17. See, e.g., the statements of the representatives of Brazil and Japan in the General Assembly's Sixth Committee A/C.6/44/SR 31, p. 5 and ibid., SR 32, p. 5.

18. A precise list of ‘Threshold Quantities of Hazardous Substances’ is to be found in OECD Council Decision C (88)84 (Final) on the exchange of information concerning accidents capable of causing transfrontier damage. Reprinted in 28 ILM (1989) p. 247. According to the ‘Interim definition’ of the term, ‘significant amounts’ for the purpose of the application of Annex II to the London Dumping Convention are ‘those amounting to more than 0.1% by weight of the waste to be dumped’. See IMCO Doc. LDC II 11 (1977) para. 71, p. 16. See also Kay, D., Jacobson, H., Environmental Protection. The International Dimension (1984) p. 127Google Scholar. More general criteria for the assessment of significance are developed within the framework of international organizations. Cf., e.g., the criteria in Appendix I (Activities likely to have significant impacts) and Appendix III (General criteria for determining environmental significance of projects) elaborated by the ECE Experts on environmental impact assessment, supra, n. 12 pp. 20–23.

19. Under the 1988 Antarctic Minerals Convention, which also adopts a ‘significant’ threshold, the impact of each planned activity has to be ‘assessed and judged acceptable’ by the Commission. The Commission will not approve an activity unless it is established that it will not have significant effects on the Antarctic environment. Cf., Arts. 1(15), 4 and 8 of the Convention on the Regulation of Antarctic Mineral Resource Activities, reprinted in 27ILM (1988) p. 868. For more details on the concept of harm adopted by the convention, see Burmester, H.C., ‘Liability for Damage from Antarctic Mineral Resource Activities’, 29 VJIL (1989) no. 3, pp 634–640Google Scholar.

20. Addressing this question, the UN International Law Commission stated that: ‘In the absence of any mathematical formula for fixing the extent to which use or enjoyment o f… water should be affected… an “appreciable extent” is proposed as the criterion. This extent is one which can be established by objective evidence… There must be a real impairment of use.’ ILC Yearbook 1980 Vol. II Part 2 p. 119. According to A. Rest, in order to prove the significance of a given transboundary impact in the absence of concrete environmental quality standards the affected State may have recourse to ‘a probability forecast based on circumstantial evidence and on the source State's past conduct’. See A. Rest, ‘Fehlende Verantwortlichkeit bei transnationalen Umweltunfälien?’, in Völkerrecht, Recht der internationalen Organisationen, Weltwirtschaftsrecht, Festschrift für I. Seidl-Hohenveldern (1988) p. 485.

21. See, e.g., the 1952 ECE study on ‘Legal aspects of hydroelectric development of rivers and lakes’ supra, n. 16; see also ILC Yearbook 1984 Vol. II Part 2 p. 330. In a similar vein – Art. 3 of the ILA ‘Salzburg Principles’ of the ILA, cited ibid., p. 202.

22. See, e.g., R. Quentin-Baxter, Third Report on International Liability, ILC Yearbook 1982 Vol. II Part 1 pp. 57–59, paras. 27, 34, 35. ‘Regional expectations’ as a criterion for establishing the significance of transboundary harm are also mentioned in the 1984 UN Secretariat's Survey of State Practice Relevant to International Liability for Injurious Consequences Arising out of Acts not Prohibited by International Law, cf., supra, n. 13, p. 106.

23. For a summary of the major developments in these topics, see ‘The Work of the International Law Commission’, fourth edition, UN Publication Sales No. E.88.V.1. pp. 100 and 117 et seq.

24. See Draft Articles 8 and 16(17) on pollution of international watercourses, S. McCaffrey, Fourth Report, 1988, A/CN.4/412/Add.2, p. 2, as well as Draft Articles 1 and 2 in Barboza's Fifth Report, ILC Yearbook 1989, A/CN.4/423, p. 10.

25. Among those ILC members who prefer the term ‘appreciable’ (as a lower threshold) are, inter alia, Hayes, Eiricsson and Francis. Cf., the summary records of the 1989 debate on the liability topic: A/CN.4/SR 2109, p. 11; SR 2112, p. 21; and SR 2111, p. 4, respectively. For opposite views (in favour of ‘significant’), cf., Ogiso, ibid. SR 2110, p. 14; Graefrath, SR 2111, p. 15; Njenga, SR 2112, p. 11; Roucounas, SR 2112, p. 15. The 1989 debate in the General Assembly's Sixth Committee was equally controversial. Among the supporters of the term ‘appreciable’ were the delegations of Australia, A/C.6/44/SR.33, p. 16; Ireland, ibid. SR 32, p. 18; Canada, SR31, p. 7. In favour of ‘significant’: USA, SR 33, p. 20; Brazil, SR 31, p. 3; Japan, SR 32, p. 7; Greece, SR 36, p. 15. A group of developing countries seem to support an extreme position according to which: ‘every harm should come within the purview of the topic’, cf., the speech from Bahrain's representative on 6 November 1989, ibid., SR 33, p. 11; and Sierra Leone, SR 31, p. 17.

26. See the commentary to Draft Article 4, ILC Yearbook 1980 Vol. II Part 2 p. 119.

27. The definition of ‘appreciable’ reads:‘…the effect or harm must have at least an impact of some consequence, for example on public health, industry, agriculture or environment in the affected system State, but not necessarily a momentuous or grave effect, in order to constitute transgression of an interest protected by international law’ ILC Yearbook 1982 Vol. II Part 1 p. 100.

28. Fourth Report, 1988, A/CN.4/412/Add.2, p.2,

29. Ibid., p. 6.

30. Ibid., note 275.

31. Cf., supra, n. 22, p. 59, paras. 34, 35 and p. 62, para. 53 (Art. 2).

32. Cf., Fifth Report 1989, A/CN.4/423, pp. 13–14, paras. 23–25, (‘appreciable risk of causing appreciable harm’, ibid., pp. 4–9).

33. Ibid., p. 14, para. 25.

34. J. Barboza, Sixth Report (1990), Doc. A/CN.4/428, p. 41.

35. Report of the ILC 1988, A/43/10, Suppl. 10, p. 62, para. 151.

36. Cf., Topical summary of the discussion held at the Sixth Committee, A/CN.4/L.443, 16 January 1990, p. 56, para. 176.

37. Interestingly, this position is also supported by the practice of Special Rapporteurs Barboza and McCaffrey who prefer the term ‘appreciable’ but quote almost exclusively sources containing the ‘significant’ threshold. Cf., McCaffrey, Fourth Report, A/CN.4/412, Add. 1 and 2, cf., also Barboza, Fifth Report, A/CN.4/423, pp. 27–32, paras. 79–95.

38. Having this in mind, it seems that the definition of ‘appreciable” by the former Special Rapporteur, S. Schwebel, is an adequate reflection of the present state of the law. It might therefore constitute a viable solution to adopt the ‘significant’ threshold and provide it with Schwebel's definition. Cf., supra, n. 27.

39. See Art. 16(2) of the WCED ‘Legal Principles and Recommendations’ and the commentary thereto, cf., supra, n. 1, p. 99 et seq.; Art. 6 of the 1989 ‘Draft American Declaration on the Environment’, supra, n. 11; and Art. II.1 of the ECE Draft Convention on Environmental Impact Assessment in a Transboundary Context, ECE ENVWA/AC.3/R.5, p. 6. See also the UNEP ‘Goals and Principles of Environmental Impact Assessment’ in UNEP Environmental Law, Guidelines and Principles No. 9 (1987) p. 1Google Scholar.

40. According to Art. 16 of the WCED ‘Legal Principles and Recommendations’ this duty arises only in the event of ‘significant risk… of causing substantial harm’. Similarly, Art. 8.1(b) of the 1987 ILA Resolution on transboundary air pollution, supra, n. 11; and Art. 12 of the ILC draft on international watercourses (‘appreciable adverse effects’). As distinct from this approach, Art. 9 of the 1989 ‘Draft American Declaration on the Environment’ (CJI/RES.II-2/89) contains a notification duty on planned measures which is not limited to potentially significant impacts. Cf., supra, n. 11.

41. Cf., Art. 19 of the WCED ‘Legal Principles and Recommendations’ supra, n. 1; Art. 11 of the Baltic Convention, supra, n. 10; Art. 8 of the London Dumping Convention, 11ILM (1972) p. 1291; as well as all regional seas conventions prepared under the auspices of the UNEP, cf., supra, n. 10. As far as the duty to warn in cases of ecological emergency is concerned, one must assume that such emergencies involve the threat of serious damage. See Art. 18 of the ILC draft on international watercourses referring to ‘a serious and immediate threat to health, life, property or water resources’, A/CN.4/412/Add. 2, p. 23.

42. This principle has gained broad acceptance. See in particular the WCED ‘Legal Principles and Recommendations’ (Art. 15); Art. 200 of the UN Law of the Sea Convention; Art. 10 of the ILC draft on international watercourses. See also Partan, D., ‘The Duty to Inform in International Environmental Law', 6 Boston University JIL (1988/1) S. 43 et seqGoogle Scholar.

43. Cf., e.g., the 1969 Brussels Convention on Civil Liability for Oil Pollution Damage (UNTS, vol. 973, p. 3) and the 1971 Convention on the Establishment of an International Fund for Compensation for Oil Pollution Damage (as amended by the 1984 Protocols), UNTS 1–17146. See Popp, A.H.E., ‘Liability and Compensation for Oil Pollution Damage Caused by Ships Revisited’, Lloyd's Maritime and Commercial LQ (1985) p. 118Google Scholar. See also Jacobsson, M. and Trotz, N., ‘The Definition of Pollution Damage in the 1984 Protocols to the 1969 Civil Liability Convention and the 1971 Fund Convention’, 17 Journal of Maritime Law and Commerce(1986) no. 4, p. 467 et seqGoogle Scholar.

44. UNTS vol. 956, p. 251.

45. Ibid., vol. 961, p. 187.

46. Cf., supran. 19.

47. In his 1990 Report on the topic of ‘Liability J. Barboza uses the terms ‘appreciable’ and ‘significant’ alternatively, see Sixth Report, A/CN.4/428/Add.l, p. 3, para 74. Art. 11 of the WCED ‘Legal Principles and recommendations’ contains a general rule on State liability for ‘significant’ harm.

48. See Art. 21 of the WCED ‘Legal Principles and Recommendations’, supra, n. 1, p. 127.

49. Opinions on this matter differ considerably. The WCED experts seem to accept the existence of general rules of international law on responsibility and liability for significant harm (cf., Arts. 11 and 21). For its part the ILC considers the drafting of such rules as a matter of ‘progressive development of international law’. Cf., the statements in the ILC during the discussion of Barboza's Fourth Report, in Report of the ILC, 40th Session, 9 May-29 July 1988, A/43/10 Suppl. 10, pp. 14–15. For a detailed analysis of the difficulties in establishing evidence of the existence of rules of customary general international law in the field of the environment, see D. Partan, loc. cit. n. 42, cf., also, Handl, G., ‘National Uses of Transboundary Air Resources: The International Entitlement Issue Reconsidered', 26 Natural Resources J. (1986) pp. 412–417Google Scholar.

50. See the debate on the matter of ‘appreciable’ at the 44th Session of the UN General Assembly, supra, n. 25. The American position was characteristic in this respect. The USA were ready to accept ‘due diligence’ responsibility for ‘appreciable’ harm in the context of international watercourses ‘… in the light… of the finite nature of what would be involved…’ At the same time they refused to accept general liability for ‘appreciable’ harm since ‘it would be another matter to admit imprecision with regard to potentially enormous liability…’ A/C.6/44/SR 33, p. 20.

51. On the specific problems connected with the application of the principles of responsibility and liability to cases of harm to global resources see, inter alia, Kiss, A., Droit International de I'Environnement (1989) p. 118Google Scholar et seq. See also the part devoted to questions of liability for harm to the ‘global commons’ in Barboza's Sixth Report, 1990, A/CN.4/428/Add.l.

52. See, e.g., the Protocols on sulphur emissions and nitrogen oxides to the 1979 ECE Convention, texts in 27 ILM (1988) p. 707 et seq., and 28 ILM (1989) p. 212 et seq., respectively; as well as the Montreal Protocol to the Ozone Convention, text in 26 ILM (1987) p. 1529.

53. This tendency seems to find further confirmation in the Draft Non-Compliance Procedure to the Montreal Protocol. Cf., Report of the first meeting of the ad hoc working group of legal experts on non-compliance with the Montreal Protocol, UNEP/OzL.Pro.Lg.l./3 July 1989. Here again, responsibility has a rather procedural character and provides for ‘measures to assist the Party's compliance’ rather than for ‘countermeasures’.