Every nation claims the right to protect its citizens from contaminated food and diseased livestock. Yet that same sovereign power can become a weapon of economic warfare, dressed in the language of public health. The WTO's Agreement on Sanitary and Phytosanitary Measures attempts to thread this needle—permitting legitimate health protection while constraining protectionist abuse. The result is one of international trade law's most intellectually demanding regimes.

The SPS Agreement occupies a unique position in trade governance. Unlike tariffs, which are transparent and easily measured, sanitary standards operate through technical regulations that can appear neutral while systematically excluding foreign products. A requirement for specific testing protocols, a ban on certain production methods, a quarantine procedure that happens to match domestic seasonal patterns—each can devastate trade flows while claiming scientific legitimacy.

What makes SPS disputes particularly fascinating is their forced marriage of law and science. WTO panels must evaluate not just legal compliance but the adequacy of scientific evidence and risk assessment methodologies. This creates institutional tensions that remain unresolved after three decades of jurisprudence. The fundamental question persists: can international trade institutions legitimately constrain how nations interpret scientific uncertainty in protecting their populations?

The SPS Agreement's Article 2.2 establishes what appears to be a straightforward principle: sanitary measures must be based on scientific principles and not maintained without sufficient scientific evidence. This language created something unprecedented in trade law—a substantive constraint on regulatory content rather than merely regulatory process or discriminatory application.

The requirement operates through a carefully constructed hierarchy. Members are encouraged to base their measures on international standards developed by bodies like the Codex Alimentarius Commission, the World Organisation for Animal Health, and the International Plant Protection Convention. Measures conforming to these standards are presumed WTO-compliant. But members retain the right to adopt higher levels of protection—provided they can demonstrate scientific justification.

This creates an immediate interpretive challenge. What does based on scientific evidence actually require? The Appellate Body has clarified that a rational relationship must exist between the measure and the scientific evidence. But science rarely speaks with one voice. Studies conflict. Methodologies vary. Expert communities disagree. The Agreement requires members to navigate this complexity while maintaining defensible positions.

The practical burden falls heavily on members defending challenged measures. They must demonstrate not just that some scientific basis exists, but that the measure rationally relates to identified risks. This evidentiary standard has proven demanding. Members have repeatedly failed to establish sufficient scientific basis for measures that domestic regulatory agencies considered well-grounded in available evidence.

The science-based requirement also creates temporal dynamics. Scientific understanding evolves. A measure justified when adopted may become indefensible as evidence accumulates—or vice versa. Article 2.2's prohibition on maintaining measures without sufficient evidence implies an ongoing obligation to reassess regulatory choices as science develops. This dynamic character distinguishes SPS obligations from static tariff commitments.

Takeaway

The SPS Agreement transforms scientific evidence from a persuasive input into regulatory decisions into a legal obligation—creating unprecedented international oversight of how nations interpret technical knowledge.

The landmark EC—Hormones dispute established foundational principles that continue shaping SPS jurisprudence. The European Communities banned beef produced with growth-promoting hormones, citing health concerns despite Codex standards permitting their use. The United States and Canada challenged the ban, initiating what became the Agreement's most influential interpretive exercise.

The Appellate Body's Hormones ruling introduced crucial distinctions. A risk assessment must evaluate the potential for adverse effects—not merely theoretical possibilities but identifiable risks arising from the specific substance or condition at issue. The assessment must be specific to the measure adopted, connecting regulatory choices to identified hazards through discernible reasoning.

Critically, the Appellate Body recognized that risk assessment involves both scientific and policy dimensions. Science identifies potential hazards and estimates probabilities. But the acceptable level of risk is a policy choice belonging to the regulating member. The SPS Agreement constrains how members evaluate risks, not what level of protection they choose. This distinction preserves regulatory sovereignty while demanding analytical rigor.

Australia—Salmon deepened the jurisprudence by examining risk assessment methodology in detail. Australia maintained quarantine restrictions on fresh salmon imports, asserting disease transmission risks. The panel and Appellate Body scrutinized whether Australia's risk assessment actually supported the measures adopted—finding critical disconnections between identified risks and regulatory responses.

The case law establishes that risk assessments must be appropriate to the circumstances—a standard that has proven remarkably demanding in application. Panels examine whether assessments address the specific products and conditions at issue, whether they evaluate risks along the entire pathway from production to consumption, and whether measures adopted rationally relate to risks identified. This granular review places substantial demands on regulatory agencies unaccustomed to having their technical work scrutinized by international tribunals.

Takeaway

WTO panels do not second-guess what level of risk nations will accept—but they intensively scrutinize whether the analytical path connecting scientific evidence to regulatory measures is rationally defensible.

The most profound unresolved tension in SPS jurisprudence concerns the precautionary principle—the proposition that regulatory action may be justified even when scientific evidence remains incomplete if potential harms are serious or irreversible. This principle enjoys widespread acceptance in environmental and health governance. Its relationship to SPS disciplines remains deeply contested.

Article 5.7 provides a provisional measures exception, permitting members to adopt precautionary measures where relevant scientific evidence is insufficient. But this exception carries demanding conditions. Members must seek additional information necessary for a more objective risk assessment and review the measure within a reasonable period. The exception treats uncertainty as a temporary condition requiring active resolution, not a permanent justification for regulatory caution.

The Appellate Body in Hormones acknowledged that the precautionary principle finds reflection in Article 5.7 and the preamble. But it declined to find that the principle had achieved the status of a general principle of international law that could override SPS obligations. This left the precautionary principle's legal status fundamentally ambiguous—recognized but not authoritative.

This ambiguity creates practical difficulties. Regulators facing genuine scientific uncertainty must navigate between two institutional pressures. Domestic populations and political systems may demand precautionary protection. WTO disciplines demand scientific justification that uncertainty, by definition, cannot provide. The institutional design assumes that good-faith regulators can distinguish between genuine uncertainty and strategic invocation of uncertainty to justify predetermined outcomes.

The deeper issue concerns institutional competence. WTO panels and the Appellate Body are legal bodies, not scientific institutions. Yet SPS jurisprudence requires them to evaluate whether scientific evidence supports regulatory measures—essentially making scientific adequacy a legal question. Critics argue this constitutes inappropriate intrusion into sovereign regulatory space. Defenders respond that some international constraint is necessary to prevent health justifications from becoming a general exception to trade liberalization commitments.

Takeaway

The SPS Agreement treats scientific uncertainty as a problem to be resolved rather than a permanent condition—creating structural tension with precautionary regulatory philosophies that view uncertainty as justifying protective action.

The SPS Agreement represents an ambitious experiment in international governance—attempting to distinguish legitimate health protection from disguised protectionism through legal scrutiny of scientific evidence. Three decades of jurisprudence have refined but not resolved the fundamental tensions inherent in this project.

What emerges is a regime that constrains regulatory behavior without eliminating regulatory discretion. Members retain sovereignty over acceptable risk levels. But they must demonstrate rational connections between scientific evidence and regulatory measures—a requirement that has proven genuinely demanding in practice.

The institutional design reflects an underlying bet: that transparent, science-based requirements can discipline regulatory choices without undermining legitimate protection. Whether this bet succeeds depends on whether trade institutions can develop sufficient scientific competence to evaluate regulatory evidence while respecting the inherent uncertainties that characterize risk governance. The jury remains out.